At regular intervals, mangoes ripen
I believe the answer is:
age
'ripen' is the definition.
(I've seen this in another clue)
'at regular intervals mangoes' is the wordplay.
'at regular intervals' indicates alternate letters.
The alternating letters of 'mangoes' are 'AGE'.
(Other definitions for age that I've seen before include "Epoch" , "Plenty of time" , "Era; grow old" , "Years since birth" , "Mature, grow in years" .)