Recess measures one metre exactly at the opening, caver finally going in (4,4)

I believe the answer is:

free time

I'm a little stuck... Click here to teach me more about this clue!

'caver finally going in' is the definition.
I can't tell whether this defines the answer.

'recess measures one metre exactly at the opening' is the wordplay.
'recess measures' becomes 'freet' (I can't justify this - if you can you should give a lot more credence to this answer).
'one' becomes 'i' (Roman numeral).
'at the opening' indicates taking the first letters.
The initial letters of 'metre exactly' is 'me'.
'freet'+'i'+'me'='FREE TIME'

Can you help me to learn more?

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.