Little time to support company function (5)
I believe the answer is:
cosec
'function' is the definition.
(mathematical function)
'little time to support company' is the wordplay.
'little time' becomes 'sec' (short for second).
'to support' is a charade indicator (letters next to each other) (in a down clue, some letters hold up others).
'company' becomes 'co' (abbreviation).
'sec' put after 'co' is 'COSEC'.
(Other definitions for cosec that I've seen before include "(In mathematics) the reciprocal of sine (abbr)" , "company secretary" , "Inverse of sine (abbr.)" , "Trig function" , "(In maths) reciprocal of sine (abbr)" .)