Not exactly yours for a time (5)
I believe the answer is:
hours
'not exactly' is the definition.
I can't tell whether this defines the answer.
'yours for a time' is the wordplay.
'yours' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'a time' becomes 'hour' (hour is a kind of time).
's' after 'hour' is 'HOURS'.
Can you help me to learn more?
(Other definitions for hours that I've seen before include "Periods of time" , "A long time" , "time appointed for work" , "Matins and Vespers, say?" .)