Follow timepiece for two hours on duty (8)
I believe the answer is:
dogwatch
'two hours on duty' is the definition.
(maritime term for a 2-hour watch)
'follow timepiece' is the wordplay.
'follow' becomes 'dog' (I've seen this before).
'timepiece' becomes 'watch' (watch is a kind of timepiece).
'dog'+'watch'='DOGWATCH'
'for' acts as a link.
(Other definitions for dogwatch that I've seen before include "Duty period for ship's complement, kind of canine alert" , "4-6pm or 6-8pm shift on a ship" , "Short afternoon shift on ship" , "short spell on board" , "period of vigil" .)