Instrument in Cambridge college keeping in time (8)
I believe the answer is:
clarinet
'instrument' is the definition.
(clarinet is a kind of instrument)
'cambridge college keeping in time' is the wordplay.
'cambridge college' becomes 'clare' (college of Cambridge University).
'keeping' is an insertion indicator (some letters kept inside).
'time' becomes 't' (abbreviation).
'clare' enclosing 'in' is 'clarine'.
'clarine'+'t'='CLARINET'
'in' acts as a link.
(Other definitions for clarinet that I've seen before include "Source of music" , "Wind instrument made from Clare tin" , "Musical wind instrument as played by Benny Goodman" , "23 instrument" , "Find an instrument in claret" .)