Alarm — time to put on slip (6)
I believe the answer is:
terror
'alarm' is the definition.
(thesaurus)
'time to put on slip' is the wordplay.
'time' becomes 't'.
'to put on' means one lot of letters go next to another.
'slip' becomes 'error' (I've seen this before).
't'+'error'='TERROR'
(Other definitions for terror that I've seen before include "consternation" , "Little brat" , "State of great fright" , "Young miscreant" , "Great fear" .)