When one's potentially had puddings, as breakfast sometimes served outside (3,5,3)
I believe the answer is:
all fools day
'outside' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for all fools day that I've seen before include "April 1st" , "First of April" , "right now" , "Significant date" .)