Paces studies, on time (6)
I believe the answer is:
treads
'paces' is the definition.
('tread' can be a synonym of 'pace')
'studies on time' is the wordplay.
'studies' becomes 'tres' (I can't explain this - if you can you should believe this answer much more).
'on' is an insertion indicator (as in clothing \'on\' a person).
'time' becomes 'ad'.
'tres' going around 'ad' is 'TREADS'.
Can you help me to learn more?
(Other definitions for treads that I've seen before include "Stared at tyre surfaces" , "mates" , "Sets the foot down." , "Puts the foot down" , "Steps, walks" .)