It doesn’t seem long when father goes by air (4,5)
I believe the answer is:
time flies
'it doesn't seem long' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'when father goes by air' is the wordplay.
I cannot quite understand how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
'goes' could be 'flies' (flying is a kind of going) and 'flies' is located in the answer.
The remaining letters 'tim' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for time flies that I've seen before include "Limits fee (anag) - proverb" , "Proverb - so life seems short" , "How quickly things move on!" .)