A friend to pass the time with (4,4)

I believe the answer is:

cell mate

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'time with' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'a friend to pass' is the wordplay.
'a friend' becomes 'mate' (mate is a kind of friend).
'to' means one lot of letters go next to another (I've seen this in other clues).
'pass' becomes 'cell' (I can't explain this - if you can you should give a lot more credence to this answer).
'mate' put after 'cell' is 'CELL MATE'.

'the' acts as a link.

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I've seen this clue in the Evening Standard.

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