Little Mark has party on time (3)
I believe the answer is:
dot
'little mark' is the definition.
(I've seen this before)
'party on time' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'on' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'do'+'t'='DOT'
'has' acts as a link.
(Other definitions for dot that I've seen before include "Speck or period" , "Small round spot" , "scatter" , "Flyspeck: period in a web address" , "Very small circular shape" .)