Advanced in fast time (4)
I believe the answer is:
lent
I believe this clue is a double definition.
'advanced' is the first definition.
(advance can mean to lend)
'fast time' is the second definition.
(a period of fasting)
'in' is the link.
(Other definitions for lent that I've seen before include "Christian penitential period" , "Forty days of fasting" , "Fast time" , "Gave for a limited period" , "Period of fasting" .)