Seeming ordinary, sober around time (10)
I believe the answer is:
ostensible
'seeming' is the definition.
('ostensible' can be a synonym of 'seeming')
'ordinary sober around time' is the wordplay.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'sober' becomes 'sensible'.
'around' indicates putting letters inside.
'time' becomes 't'.
'sensible' placed around 't' is 'stensible'.
'o'+'stensible'='OSTENSIBLE'
(Other definitions for ostensible that I've seen before include "Apparently true" , "Manifest" , "Supposed" , "Professed" , "Seeming" .)