Reserve time to visit coast (3,5)
I believe the answer is:
set aside
'reserve' is the definition.
('set aside' can be a synonym of 'reserve')
'time to visit coast' is the wordplay.
'time' becomes 't'.
'to visit' means one lot of letters goes inside another.
'coast' becomes 'seaside' (I've seen this before).
't' going inside 'seaside' is 'SET-ASIDE'.
(Other definitions for set aside that I've seen before include "Save or discard" , "Fallow" , "Policy for leaving land alone" , "Lay by" , "kept for later" .)