When to expect moisture, it’s said, on fruit (3,4)
I believe the answer is:
due date
'when to expect' is the definition.
(when a baby is due)
'moisture it's said on fruit' is the wordplay.
'moisture' becomes 'dew' (I have seen 'Overnight moisture ' mean 'dew' so perhaps 'moisture' could also mean 'dew').
'it's said' indicates a 'sounds like' (homophone) clue.
'on' means one lot of letters go next to another.
'fruit' becomes 'date' (date is a kind of fruit).
'dew' is a homophone of 'due'.
'due'+'date'='DUE DATE'
(Another definition for due date that I've seen is " Term".)