Second time split for Labour (6)
I believe the answer is:
strive
'labour' is the definition.
(striving is a kind of labouring)
'second time split' is the wordplay.
'second' becomes 's' (common abbreviation).
'time' becomes 't'.
'split' becomes 'rive' ('rive' can be a synonym of 'split'**).
's'+'t'+'rive'='STRIVE'
'for' is the link.
(Other definitions for strive that I've seen before include "Exert much effort" , "Work hard - compete" , "Make a great effort" , "Try hard, carry on conflict" , "Make every effort" .)