To give relief around the first of December is too long to wait (3,3)
I believe the answer is:
all day
'too long to wait' is the definition.
I can't tell whether this defines the answer.
'to give relief around the first of december' is the wordplay.
'to give relief' becomes 'allay' (I can't explain this - if you can you should believe this answer much more).
'around' is an insertion indicator.
'the first of december' becomes 'd' (ast letter of 'december').
'allay' enclosing 'd' is 'ALL-DAY'.
'is' is the link.
Can you help me to learn more?
(Other definitions for all day that I've seen before include "morning and afternoon" , "until even" , "From dawn to dusk" .)