Sometimes twice! (3,3,5)
I believe the answer is:
now and again
'sometimes' is the definition.
(I've seen this before)
'twice' is the wordplay.
I cannot quite understand how this works, but
'twice' could be 'again' (I've seen this in another clue) and 'again' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for now and again that I've seen before include "From time to time" , "Occasionally" , "Sometimes" .)