Advanced fast (4)
I believe the answer is:
lent
This clue is a double definition.
'advanced' is the first definition.
(advance can mean to lend)
'fast' is the second definition.
(Lent is a period of fasting in Christianity)
(Other definitions for lent that I've seen before include "Christian penitential period" , "Period from Ash Wednesday to Easter" , "Pre-Easter period" , "days before Easter" , "Christian period of abstinence" .)