Dorothy! It's party time! (3)
I believe the answer is:
dot
'dorothy' is the definition.
(nickname for someone called Dorothy)
'party time' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'time' becomes 't' (abbreviation).
'do'+'t'='DOT'
'it's' acts as a link.
(Other definitions for dot that I've seen before include "Very small circular shape" , "A point, small round mark" , "Tiny speck" , "Long-ago year?" , "Flyspeck: period in a web address" .)