To be enjoyed when one's fairly tired? (3,5,2,3,4)

'to be enjoyed' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'one's fairly tired?' is the wordplay.
I cannot really see how this works, but
'one's' could be 'thes' (both can introduce a definite example of something) and 'thes' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

'when' is the link.

Can you help me to learn more?