Pleasure trips must start late for these relations (5)
I believe the answer is:
aunts
'these relations' is the definition.
(aunt is a kind of relation)
'pleasure trips must start late' is the wordplay.
'pleasure trips' becomes 'jaunts' ('jaunt' can be a synonym of 'pleasure trip').
'must start late' means to remove the first letter.
'jaunts' with its first letter taken away is 'AUNTS'.
'for' is the link.
(Other definitions for aunts that I've seen before include "Parents' sisters" , "Sally and others" , "Elderly female relations" , "Relatives get a peculiar US tan" , "Female relatives, usually older" .)