In case you haven't guessed, this is a work in progress.
Unit	Length, Duration and Size	Notes	Other
xentojiffy (physics)	-3(1053s)	The amount of time it hypothetically takes light to hypothetically travel one Fermi (hypothetically the size of a nucleon) in a vacuum. This is the shortest time unit hypothetically possible to understand in physics. All hypothetically smaller time units have no hypothetical use in physics.
yoctojiffy (physics)	3(10-49s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
zeptojiffy (physics)	3(10-46s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
Planck time unit	5.39(10-44 s	The amount of time light takes to travel one Planck length.
attojiffy (physics)	3(10-43s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
femtojiffy (physics)	3(10-40s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
picojiffy (physics)	3(10-37s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
nanojiffy (physics)	3(10-34s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
myriojiffy (physics)	3(10-31s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
millijiffy (physics)	3(10-29s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
xentojiffy (electronics)	1/6(1028 s to 1/5(1028 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
millijiffy (physics)	3(10-28s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
xentosecond	10-27 s
centijiffy (physics)	3(10-27s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
xentominute	6 x 10-26 s
yoctojiffy (electronics)	1/6 x 1025 s to 1/5 x 1025 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
decijiffy (physics)	3(10-25s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
yoctosecond	10-24 s
jiffy (physics)	3(10-24s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
decajiffy (physics)	3(10-23s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
xentohour	3.6 x 10-24 s
yoctominute	6 x 10-23 s
xentoday	8.64 x 10-23 s
zeptojiffy (electronics)	1/6 x 1022 s to 1/5 x 1022 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
hectojiffy (physics)	3(10-22s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
xentoweek	6.048 x 10-22 s
zeptosecond	10-21 s
xentomonth	2.62974(10-21s
kilojiffy (physics)	3(10-21s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
yoctohour	3.6 x 10-21 s
xentoannum	10-27 years	31.5569 zeptoseconds
zeptominute	6 x 10-20 s
yoctoday	8.64 x 10-20 s
attojiffy (electronics)	1/6 x 1019 s to 1/5 x 1019 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
yoctoweek	6.048 x 10-19 s
attosecond	10-18 s	shortest time now measurable
yoctomonth	2.62974(10-18s
megajiffy (physics)	3(10-18s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
zeptohour	3.6 x 10-18 s
yoctoannum	10-24 years	31.5569 attoseconds
attominute	6 x 10-17 s
zeptoday	8.64 x 10-17 s	get gotted
femtojiffy (electronics)	1/6 x 1016 s to 1/5 x 1016 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
zeptoweek	6.048 x 10-16 s
femtosecond	10-15 s	pulse time on fastest lasers
zeptomonth	2.62974(10-15s
gigajiffy (physics)	3(10-15s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
attohour	3.6 x 10-15 s
zeptoannum	10-21 years	31.5569 femtoseconds
femtominute	6 x 10-14 s
attoday	8.64 x 10-14 s
picojiffy (electronics)	1/6 x 1013 s to 1/5 x 1013 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
svedberg	1 x 10-13 s	Time unit used for sedimentation rates (usually of proteins).
attoweek	6.048 x 10-13 s
picosecond	10-12 s
attomonth	2.62974(10-12s
terajiffy (physics)	3(10-12s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
femtohour	3.6 x 10-12 s
attoannum	10-18 years	31.5569 picoseconds
picominute	6 x 10-11 s
femtoday	8.64 x 10-11 s
nanojiffy (electronics)	1/6 x 1010 s to 1/5 x 1010 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
femtoweek	6.048 x 10-10 s
nanosecond	10-9 s	time for molecules to fluoresce
femtomonth	2.62974(10-9s
petajiffy (physics)	3(10-9s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
picohour	3.6 x 10-9 s
femtoannum	10-15 years	31.5569 nanoseconds
shake	10-8 s	Also a casual term for a short period of time	10 nanoseconds
nanominute	6 x 10-8 s
picoday	8.64 x 10-8 s
microjiffy (electronics)	1/6 x 107 s to 1/5 x 107 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
picoweek	6.048 x 10-7 s
microsecond	10-6 s
picomonth	2.62974(10-6s
exajiffy (physics)	3(10-6s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
nanohour	3.6 x 10-6 s
fifth	4.63 x 10-6 s	medieval unit of time
picoannum	10-12 years	31.5569 microseconds
myriojiffy (electronics)	1/600000 s to 1/500000 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
microminute	6 x 10-5 s
nanoday	8.64 x 10-5 s
myriosecond	0.0001 s	shortest time unit used on stopwatches
millijiffy (electronics)	1/60000 s to 1/50000 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
fourth	1/3,600 second	medieval unit of time
nanoweek	6.048 x 10-4 s
millisecond	0.001 s	shortest time unit used on stopwatches
nanomonth	0.00262974 s
zettajiffy (physics)	0.003 s	The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
myriominute	0.006 s
centijiffy (electronics)	1/6000 s to 1/5000 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
microhour	0.0036 s	3 milliseconds and 6 microseconds
centisecond	0.01 s	used on some stopwatches
dwink	0.0185 s	commonly found on the internet
decijiffy (electronics)	1/600 s to 1/500 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
third	1/60 s	medieval unit of time
nanoannum	10-9 years	31.5569 milliseconds
milliminute	0.06 s
microday	0.0864 seconds
decisecond	0.1 s	used on some stopwatches
jiffy (electronics)	1/60 s to 1/50 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
bijiffy (electronics)	1/30 s to 1/25 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
trijiffy (electronics)	1/20 s to 1/10 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
quadjiffy (electronics)	4/60 s to 4/50 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
quintjiffy(electronics)	5/60 s to 5/50 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
wink	0.222 seconds	commonly found on the internet
myriohour	0.36 seconds
semisecond	0.5 seconds
centiminute	0.6 s
microweek	0.6048 s
second / unisecond / leap second	1 s	SI base unit
decajiffy (electronics)	1/6 s to 1/5 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
bisecond	2 seconds
micromonth	2.62974 s
trisecond	3 seconds
millihour	3.6 seconds
quadrasecond / tetrasecond	4 seconds
quintsecond / pentasecond	5 seconds
deciminute / hexasecond	6 seconds
heptasecond	7 seconds
instant / octasecond	8 seconds	commonly found on the internet
myrioday	8.64 seconds
nonasecond	9 seconds
decasecond	10 seconds
hectojiffy (electronics)	10/6 s to 2 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
hendecasecond	11 seconds
dodecasecond	12 seconds
triadecasecond	13 seconds
tessaradecasecond	14 seconds
quindecasecond / pentedecasecond	15 seconds
vigintisecond	20 seconds
trigintisecond	30 seconds
microannum	10-6 years	31.5569 seconds
centihour	36 seconds
quadragintisecond	40 seconds
quinquagintisecond	50 seconds
minute60 seconds
septagintisecond	70 seconds
myrioweek	1.008 minutes
octingintisecond	80 seconds
milliday	86.4 seconds	About 1 minute and 26.4 seconds
moment	90 seconds	medieval unit of time
hectosecond	100 seconds	1 minute and 40 seconds
myriomonth	0.0001 months
biminute	2 minutes
kilojiffy (electronics)	100/6 s to 20 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time
triminute	3 minutes
duhectosecond	200 seconds	3 minutes and 20 seconds
quadraminute	4 minutes
quintminute	5 minutes
decihour	6 minutes
octminute	8 minutes
dekaminute	10 minutes
milliweek	10.08 minutes
ke	14 minutes and 24 seconds	Also called centiday
tide	15 minutes
kilosecond	1,000 seconds	16 minutes and 40 seconds
vigintiminute	20 minutes
trigintiminute	30 minutes
millimonth	0.001 months
myrioannum	0.0001 years
hour60 minutes
hectominute	100 minutes	1 hour and 40 minutes
centiweek	1.68 hours	1 hour and 48 minutes
bihour	2 hours
deciday	2.4 hours	2 hours and 24 minutes
myriasecond	10,000 seconds	2 hours, 46 minutes and 40 seconds
trihour	3 hours
nune	3.5 hours	commonly found on the internet
megajiffy (electronics)	100000/6 s to 20000 s	Used to measure the time between alternating power cycles. Also a casual term for a short period of time	4.62963 hours
quinthour	5 hours
sexahour	6 hours
centimonth	0.01 months	7.3048439814815 hours
milliannum	0.001 years	8.76581 hours
dekahour	10 hours
demiday	12 hours
kilominute	1,000 minutes	16 hours and 40 minutes
deciweek	16.8 hours	16 hours and 48 minutes
day24 hours	longest unit used on stopwatches and countdowns	1 day or 24 hours
biday	2 days
triday	3 days
decimonth	0.1 months	3.04368 days
centiannum	0.01 years	3.65242 days
quadraday	4 days
hectohour	100 hours	4 days and 4 hours
pentaday	5 days
myriaminute	10,000 minutes
week7 days	Also called sennight
dekaday	10 days	10 days
megasecond	1,000,000 seconds	About 11.6 days
fortnight	2 weeks	14 days	may not be common
lunar month	27 Days 4 hours 48 minutes to 29 days 12 hours	Various definitions of lunar month exist.
quadraweek	28 days
month28 to 31 days	30.4368 days
deciannum	1.2 months or 36.5 days	1 month, 5 to 8 days, and 12 hours
kilohour	1,000 hours	1 month, 13 to 16 days, and 16 hours
dekaweek	70 days / 10 weeks
quarter and season	3 months	It is called season if it is based on TV or weather temperature, otherwise it is called quarter
hectoday	100 days	3 months and 8 to 11 days
decafortnight	140 days	4 months and 20 days (assuming 30 days per month)
dekamonth	10 months
novemquadraweek	49 weeks	was mentioned in metric time
duodekamonth	12 months
year12 months or 365 days
common year / original year / non-leap year / normal year / no leap year / exceptional common year / non-century leap year / no century leap year	365 days	52 weeks + 1 day
tropical year	365 days 5:48:45.216 hours	average
Gregorian year	365 days 5:49:12 hours	average
sidereal year	365 days 6:09:09.7635456 hours
non-leap year	365.24 days
mean year	365.25 days
Julian year	365.3 days
leap year / non-common year / no common year / century leap year / intercalary year / bissextile year / non-exceptional common year / no exceptional common year	366 days	52 weeks + 2 days
myriahour	10,000 hours
hectoweek	700 days / 100 weeks
tricosamonth	23 months
biennium	2 years	A unit of time commonly used by legislatures
megaminute	1,000,000 minutes	About 696 days
kiloday	1,000 days	2 years, 8 months, 27 days the other
triennium	3 years
leap cycle	3 common years
quadrennium	4 years
lustrum / quinquennium	5 years
sexennium	6 years
septennium	7 years
octennium	8 years
hectomonth	100 months	About 8 years and 4 months
novennium	9 years
decade	10 years
Indiction / quindecennium	15 years
generation	17-35 years
kiloweek	7,000 days / 1,000 weeks
score	20 years
myriaday	10,000 days
gigasecond	1,000,000,000 seconds	About 31.7 years
jubilee	50 years
kilomonth	1,000 months	About 83 years and 4 months
century	100 years
megahour	1,000,000 hours	About 114.12 years
bicentennium	200 years
tricentenium	300 years
myriaweek	70,000 days / 10,000 weeks
myriamonth	10,000 months
millennium	1,000 years	also called "kiloannum"
gigaminute	1,000,000,000 minutes	About 1,902 years
megaday	1,000,000 days	About 2,737.918 years
myriaannum / deca-millennium	10,000 years
megaweek	7,000,000 days / 1,000,000 weeks
terasecond	1 trillion seconds	About 31,700 years
megamonth	1,000,000 months	About 83,000 years and 4 months
deca-myriaannum / centa-millennium	100,000 years
gigahour	1,000,000,000 hours	About 114,120 years
age and megaannum	1,000,000 years
teraminute	1 trillion minutes	About 1,902,000 years
gigaday	1,000,000,000 days	About 2,737,918 years
epoch	10,000,000 years
gigaweek	7,000,000,000 days / 1,000,000,000 weeks
petasecond	1 quadrillion seconds	About 3.17 epochs
gigamonth	1,000,000,000 months	About 83,000,000 years and 4 months
era	100,000,000 years
terahour	1 trillion hours	About 114,120,000 years
galactic year	Approximately 2.3 eras	The amount of time it takes the Solar System to orbit the center of the Milky Way Galaxy one time.
eon	500,000,000 years	Also "An indefinite and very long period of time"
gigaannum	1,000,000,000 years
petaminute	1 quadrillion minutes	About 1,902,000,000 years
teraday	1,000,000,000,000 days	About 2,737,918,000 years
teraweek	7 trillion days / 1 trillion weeks
exasecond	1 quintillion seconds	roughly 31.7 billion years, more than twice the age of the universe on current estimates
teramonth	1,000,000,000,000 months	About 83,000,000,000 years and 4 months
petahour	1 quadrillion hours	About 114,120,000,000 years
teraannum	1 trillion years
examinute	1 quintillion minutes	About 1.902 trillion years
petaday	1 quadrillion days	About 2,737,918,000,000 years
petaweek	7 quadrillion days / 1 quadrillion weeks
zettasecond	1 sextillion seconds	About 31.7 trillion years
petamonth	1 quadrillion months	About 83,000,000,000,000 years and 4 months
exahour	1 quintillion hours	About 1.1412 x 1014 years
petaannum	1 quadrillion years
zettaminute	1 sextillion minutes	About 1.902 quadrillion years
exaday	1 quintillion days	About 2.737918 quadrillion years
exaweek	7 quintillion days / 1 quintillion weeks
yottasecond	1 septillion seconds	About 31.7 quadrillion years
examonth	1 quintillion months	About 83 quadrillion years and 4 months
zettahour	1 sextillion hours	About 1.1412 x 1017 years
exaannum	1 quintillion years
yottaminute	1 septillion minutes	About 1.902 quintillion years
zettaday	1 sextillion days	About 2.737918 quintillion years
zettaweek	7 sextillion days / 1 sextillion weeks
xennasecond	1 octillion seconds	About 31.7 quintillion years
zettamonth	1 sextillion months	About 83 quintillion years and 4 months
yottahour	1 septillion hours	About 1.1412 x 1020 years
zettaannum	1 sextillion years
xennaminute	1 octillion minutes	About 1.902 sextillion years
yottaday	1 septillion days	About 2.737918 sextillion years
yottaweek	7 septillion days / 1 septillion weeks
dakasecond	1 nonillion seconds	About 31.7 sextillion years
yottamonth	1 septillion months	About 83 sextillion years and 4 months
xennahour	1 octillion hours	About 1.1412 x 1023 years
yottaannum	1 septillion years
hendasecond	1 decillion seconds	About 31.7 septillion years
dakaminute	1 nonillion minutes	About 1.902 septillion years
xennaaday	1 octillion days	About 2.737918 septillion years
xennaweek	7 octillion days / 1 octillion weeks
xennamonth	1 octillion months	About 83 septillion years and 4 months
dakahour	1 nonillion hours	About 1.1412 x 1026 years
xennannum	1 octillion years
hendaminute	1 decillion minutes	About 1.902 octillion years
dakaday	1 nonillion days	About 2.737918 octillion years
dakaweek	7 nonillion days / 1 nonillion weeks
dakamonth	1 nonillion months	About 83 octillion years and 4 months
hendahour	1 decillion hours	About 1.1412 x 1029 years
dakaannum	1 nonillion years
hendaaday	1 decillion days	About 2.737918 nonillion years
hendaweek	7 decillion days / 1 decillion weeks
cosmological decade / deca-dakaannum	10 nonillion years	10 times the length of the previou cosmological decade, with CD1 beginning either 10 seconds or 10 years after the Big Bang, depending on the definition. This is the longest time unit possible to understand in physics. All longer time units have no use in physics.
hendamonth	1 decillion months	About 83 nonillion years and 4 months
deca-cosmological decade / centa-dakaannum	100 nonillion years
hendaannum	1 decillion years
decillion	is equal to 1 followed by 33 zeros, or a billion trillion trillions
quindecillion	it's equal to 1 followed by 48 zeros, or a trillion trillion trillion trillions
multicosmological year / melleni-cosmological decade	1 tredecillion years