Being out on one's feet? (14)

I believe the answer is:

noctambulation

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

'being out' is the definition.
The definition suggests a singular noun which matches the answer.

'on one's feet?' is the wordplay.
I cannot quite see how this works, but
'on' could be 'at' (I've seen this in other clues) and 'at' is found within the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Independent.

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