Fast time finishing final race in first (4)
I believe the answer is:
lent
'fast time' is the definition.
(a period of fasting)
'finishing final race in first' is the wordplay.
'finishing' suggests the final letters (the letter which finishes the word).
The final letters of 'final race in first' are 'LENT'.
(Other definitions for lent that I've seen before include "Christian penitential season" , "Christian penitential period" , "Loaned; a fast" , "Period of penance" , "Provided loans" .)