The twenty-four hours without food will be over in no time! (4,3)

'the twenty-four hours' is the definition.
The answer and definition can be both related to time as well as being singular nouns.
Perhaps you can see an association between them that I can't see?

'without food will be over in no time' is the wordplay.
I cannot really see how this works, but
'food' could be 'd' (D is an example) and 'd' is present in the answer.
'be' could be 'stay' (staying is a kind of being) and 'stay' is present in the remaining letters.
The remaining letters 'fa' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?