Thirty days in Capri? Lovely! (5)
I believe the answer is:
april
'thirty days' is the definition.
(I've seen this before)
'in capri? lovely' is the wordplay.
'in' indicates a hidden word.
'APRIL' can be found hidden inside 'capri lovely'.
(Other definitions for april that I've seen before include "whose first date is foolish?" , "period of time" , "Month of showers and of the Queen's birthday" , "Thirty days in spring" , "Fourth month" .)