Work until 1.50 (4)
I believe the answer is:
toil
'work' is the definition.
(toil is a kind of work)
'until 1 50' is the wordplay.
'until' becomes 'to' (I've seen this in other clues).
'1' becomes 'i' (roman numeral).
'50' becomes 'l' (roman numeral).
'to'+'i'+'l'='TOIL'
(Other definitions for toil that I've seen before include "Work really hard" , "Manual labour" , "Work incessantly" , "Work hard, labour" , "Work extremely hard" .)