Heaven is in March (8)
I believe the answer is:
paradise
'heaven' is the definition.
(I know that Paradise is a type of heaven)
'is in march' is the wordplay.
'in' is an insertion indicator.
'march' becomes 'parade' (synonyms).
'is' placed inside 'parade' is 'PARADISE'.
(Other definitions for paradise that I've seen before include "Heaven, nirvana, Valhalla etc" , "Shangri-La?" , "blissful place?" , "park" , "Felicity" .)