May possibly have chanted normal version (8,5)
I believe the answer is:
calendar month
'may possibly' is the definition.
(may is a kind of calendar month)
'chanted normal version' is the wordplay.
'version' indicates anagramming the letters.
'chanted'+'normal'='chantednormal'
'chantednormal' is an anagram of 'CALENDAR MONTH'.
'have' acts as a link.
(Other definitions for calendar month that I've seen before include "May perhaps" , "all the May days?" , "several weeks" , "May, for instance" , "Twelfth of the year" .)