It's a long time for one to dally foolishly (3,3)
I believe the answer is:
all day
'it's a long time' is the definition.
I can't tell whether this defines the answer.
'one to dally foolishly' is the wordplay.
I cannot really see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
an anagram of 'dally' is 'llday' which is within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for all day that I've seen before include "morning and afternoon" , "From dawn to dusk" , "until even" .)