All set for about a day, perhaps (5)
I believe the answer is:
ready
'all set' is the definition.
(I've seen this before)
'about a day perhaps' is the wordplay.
'about' becomes 're' (regarding).
'perhaps' indicates anagramming the letters.
'day' is an anagram of 'ady'.
're'+'ady'='READY'
'for' acts as a link.
(Other definitions for ready that I've seen before include "At hand" , "Prepare < dough" , "Prepare money" , "Willing (to do something), prepare" , "Available now" .)