Spare time not disguised (5)
I believe the answer is:
overt
'not disguised' is the definition.
(I've seen this before)
'spare time' is the wordplay.
'spare' becomes 'over' (left over).
'time' becomes 't' (abbreviation).
'over'+'t'='OVERT'
(Other definitions for overt that I've seen before include "Openly displayed" , "Open, not secret or hidden" , "Done in an obvious way" , "Obvious, patent" , "Clear" .)