Made an advance fast (4)
I believe the answer is:
lent
This clue is a double definition.
'made an advance' is the first definition.
'fast' is the second definition.
(I've seen this before)
(Other definitions for lent that I've seen before include "Gave for a limited period" , "From Ash Wednesday to Holy Saturday" , "Christian penitential period" , "Christian penitential season" , "Period of fasting" .)