Not exactly yours for a time (5)
I believe the answer is:
hours
'not exactly yours for a time' is the definition.
I can't tell whether this definition defines the answer.
'yours for a time' is the wordplay.
'yours' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'for' says to put letters next to each other (I've seen this in other clues).
'a time' becomes 'hour' (unit of time).
's' put 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?" .)