Heavenly place is locked up in March (8)
I believe the answer is:
paradise
'heavenly place' is the definition.
(heaven is paradise)
'is locked up in march' is the wordplay.
'locked up in' is an insertion indicator.
'march' becomes 'parade' (synonyms).
'is' inserted within 'parade' is 'PARADISE'.
(Other definitions for paradise that I've seen before include "a state of bliss" , "Felicity" , "limbo" , "Shangri-La?" , "What was lost to the poet" .)