Time to nip in for one holiday (4)
I believe the answer is:
stay
'for one holiday' is the definition.
(thesaurus)
'time to nip in' is the wordplay.
'time' becomes 't' (abbreviation).
'to nip' becomes 'say' (I can't explain this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
't' going inside 'say' is 'STAY'.
Can you help me to learn more?
(Other definitions for stay that I've seen before include "Stick around" , "Remain; guy" , "Remain behind" , "Check" , "Visit (for the night)" .)