Long period of time before end of season (5)
I believe the answer is:
yearn
'long' is the definition.
('yearn' can be a synonym of 'long')
'period of time before end of season' is the wordplay.
'period of time' becomes 'year' (year is a kind of period of time**).
'before' means one lot of letters go next to another.
'end of' indicates one should take the final letters.
The final letter of 'season' is 'n'.
'year'+'n'='YEARN'
(Other definitions for yearn that I've seen before include "Curdle" , "Have a great longing" , "Mark of injury" , "Have a craving" , "Have strong desire" .)