As far as “a day boy” (3)

I believe the answer is:

tod

'boy' is the definition.

'as far as a day' is the wordplay.
'as far as' becomes 'to'.
'a day' becomes 'd' (abbreviation for day).
'to'+'d'='TOD'

(Other definitions for tod that I've seen before include "If you're on it, you're on your own" , "Sly person" , "One's alone on this" , "Fox" , "Former English weight for wool - dot it" .)

I've seen this clue in the Evening Standard.

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