When?

ephemera
something transitory; lasting a day
 
sudden death
(sports) overtime in which play is stopped as soon as one contestant scores; e.g. football and golf
 
century
a period of 100 years
 
Middle Paleolithic
the time period of Neanderthal man; ended about 35,000 years BC
 
silly season
a time usually late summer characterized by exaggerated news stories about frivolous matters for want of real news
 
degree day
the day on which university degrees are conferred
 
Guy Fawkes Day
day for the celebration of the discovery of the Gunpowder Plot
 
Discovery Day
a legal holiday commemorating the discovery of America by Christopher Columbus
 
dogwatch
either of two short watches: from 4-6 pm or 6-8 pm
 
usance
the period of time permitted by commercial usage for the payment of a bill of exchange (especially a foreign bill of exchange)
 
Passion Sunday
second Sunday before Easter
 
mid-December
the middle part of December
 
forenoon
the time period between dawn and noon
 
present times
the circumstances and ideas of the present age
 
grace
a period of time past the deadline for fulfilling an obligation during which a penalty that would be imposed for being late is waived, especially an extended period granted as a special favor
 
golden age
any period (sometimes imaginary) of great peace and prosperity and happiness
 
social season
the season for major social events
 
Dhu al-Hijjah
the twelfth month of the Islamic calendar and the season of the hajj; has one extra day in leap years
 
times
a more or less definite period of time now or previously present
 
reign
the period during which a monarch is sovereign
 
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