Time for a big event (1-3)
I believe the answer is:
d-day
'time for a big event' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for d-day that I've seen before include "June 6, 1944" , "6.6.44" , "World War Two Normandy landings date" , "Allied landings date" , "'June 6th, 1944 (1-3)'" .)