Mark needs to complete on time (3)
I believe the answer is:
dot
'mark' is the definition.
(dotting is a kind of marking)
'to complete on time' is the wordplay.
'to complete' becomes 'do' (doing is a kind of completing).
'on' says to put letters next to each other.
'time' becomes 't'.
'do'+'t'='DOT'
'needs' is the link.
(Other definitions for dot that I've seen before include "One of the signals in Morse code" , "A point, small round mark" , "Very small circular shape" , "Cotton, say" , "scatter" .)