Perhaps watch sphere from the south (5)
I believe the answer is:
timer
'perhaps watch' is the definition.
(a watch times things)
'sphere from the south' is the wordplay.
'sphere' becomes 'remit' (both can mean someone's area of work or activity).
'from the south' says the letters should be written in reverse (in a down clue, letters go up).
'remit' written backwards gives 'TIMER'.
(Other definitions for timer that I've seen before include "Remit for, say, measuring device - or the measurer (5)" , "Stopwatch, say" , "One may be alarmed" , "Maybe watch" , "Preset mechanisation to activate a device" .)