A short stretch of time criminal tries to reduce gradually (8)
I believe the answer is:
amortise
'reduce gradually' is the definition.
'a short stretch of time criminal tries' is the wordplay.
'short stretch of time' becomes 'mo' (mo can mean a very short amount of time).
'criminal' indicates anagramming the letters.
'tries' anagrammed gives 'rtise'.
'a'+'mo'+'rtise'='AMORTISE'
'to' acts as a link.
(Other definitions for amortise that I've seen before include "Liquidate gradually" , "Gradually write off initial costs" .)