Crossword Genius

I am leaving to find out how long Rossini opera lasts? We'll see (4,4,4)

Ross

I believe the answer is:

time will tell

'we'll see' is the definition.
(both can mean something will be known eventually)

'i am leaving to find out how long rossini opera lasts?' is the wordplay.
I cannot really understand how this works, but
'i' could be 'me' and 'me' is found in the answer.
'long' could be 'l' and 'l' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

(Other definitions for time will tell that I've seen before include "Results are only to be clarified in the future" , "Wait and see" , "You must be patient" , "Try to measure speed of arrow" .)

I've seen this clue in The Times.
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