In time, split with your leader (6)
I believe the answer is:
trendy
'in' is the definition.
(thesaurus)
'time split with your leader' is the wordplay.
'time' becomes 't'.
'split' becomes 'rend' (I've seen this before**).
'with' means one lot of letters go next to another.
'leader' indicates taking the first letters.
The first letter of 'your' is 'y'.
't'+'rend'+'y'='TRENDY'
(Other definitions for trendy that I've seen before include "In accordance with the latest fad" , "Cool" , "Smart" , "Voguish" , "With it, a la mode" .)