All set for about a day, perhaps (5)
I believe the answer is:
ready
'all set' is the definition.
(thesaurus)
'about a day perhaps' is the wordplay.
'about' becomes 'rea' (I've seen this in other clues**).
'a day' becomes 'd'.
'perhaps' becomes 'y' (I've seen this in other clues).
'rea'+'d'+'y'='READY'
'for' is the link.
(Other definitions for ready that I've seen before include "At hand" , "Prepare < dough" , "Prepare money" , "Willing (to do something), prepare" , "Available now" .)