How Doris signed on a significant time in 1944 (1-3)
I believe the answer is:
d-day
'signed on a significant time in 1944' is the definition.
I can't judge whether this defines the answer.
'how doris' is the wordplay.
I cannot quite see how this works, but
'doris' could be 'day' (actress Doris Day is an example) and 'day' is located in the answer.
A single letter 'd' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for d-day that I've seen before include "'June 6th, 1944 (1-3)'" , "Launch date" , "Tricky landings" , "Invasion of Europe start" , "6.6.44" .)