Reserve short time in holiday place (3,5)
I believe the answer is:
set aside
'reserve' is the definition.
('set aside' can be a synonym of 'reserve')
'time in holiday place' is the wordplay.
'time' becomes 't'.
'in' is an insertion indicator.
'holiday place' becomes 'seaside' (I've seen this before).
't' inserted within 'seaside' is 'SET-ASIDE'.
'short' acts as a link.
(Other definitions for set aside that I've seen before include "Save or discard" , "Lay by" , "not productive land" , "Reserve(d) in advance" , "Fallow" .)