When?

April
the month following March and preceding May
 
Iyyar
the eighth month of the civil year; the second month of the ecclesiastical year (in April and May)
 
mid-January
the middle part of January
 
1780s
the decade from 1780 to 1789
 
Nissan
the seventh month of the civil year; the first month of the ecclesiastic year (in March and April)
 
silver jubilee
an anniversary celebrating the passage of 25 years
 
uptime
a period of time when something (as a machine or factory) is functioning and available for use
 
February 29
the name of the day that is added during a leap year
 
turn of the century
the period from about ten years before to ten years after a new century
 
Commonwealth Day
British, anniversary of Queen Victoria's birth
 
Thanksgiving Day
fourth Thursday in November in the United States; second Monday in October in Canada; commemorates a feast held in 1621 by the Pilgrims and the Wampanoag
 
year
the period of time that it takes for a planet (as, e.g., Earth or Mars) to make a complete revolution around the sun
 
Feast of Dormition
celebration in the Eastern Orthodox Church of the Virgin Mary's being taken up into heaven when her earthly life ended; corresponds to the Assumption in the Roman Catholic Church and is also celebrated on August 15th
 
Harlem Renaissance
a period in the 1920s when African-American achievements in art and music and literature flourished
 
eventide
the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)
 
run
the continuous period of time during which something (a machine or a factory) operates or continues in operation
 
incubation period
the period between infection and the appearance of symptoms of the disease
 
semester
one of two divisions of an academic year
 
Stone Age
(archeology) the earliest known period of human culture, characterized by the use of stone implements
 
jubilee
a special anniversary (or the celebration of it)
 
  List More