Time students must be backed with increase? (7)
I believe the answer is:
sunrise
'time' is the definition.
(sunrise is a kind of time)
'students must be backed with increase?' is the wordplay.
'students' becomes 'nus' (I've seen this in other clues).
'must be backed' says the letters should be written in reverse.
'with' means one lot of letters go next to another.
'increase?' becomes 'rise' (rise is a kind of increase).
'nus' written backwards gives 'sun'.
'sun'+'rise'='SUNRISE'
(Other definitions for sunrise that I've seen before include "Dawning of the day" , "See 21" , "Time of full daylight" , "Daybreak" , "Day's beginning" .)