Marsupials have time to settle down (5)
I believe the answer is:
roost
'settle down' is the definition.
(roosting is a kind of settling down)
'marsupials have time' is the wordplay.
'marsupials have' becomes 'roos' (I am not sure about this - if you are sure you should believe this answer much more).
'time' becomes 't' (abbreviation).
'roos'+'t'='ROOST'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for roost that I've seen before include "Place on which bird rests" , "somewhere to sleep" , "Shetland tidal water" , "Torso (anag)" , "Fowl's perch" .)