See about painter turning up ahead of time (5)
I believe the answer is:
Here is my best explanation:
'ahead of time' is the definition.
('early' can be a synonym of 'ahead of time')
'see about painter turning up' is the subsidiary indication.
'see' becomes 'ely' (example where cathedral located in diocese**).
'about' means one lot of letters goes inside another.
'painter' becomes 'ra'.
'turning up' says the letters should be written backwards.
'ra' backwards is 'ar'.
'ely' placed around 'ar' is 'early'.
(Other definitions for early that I've seen before include "in the morning?", "Beforehand", "New-season", "This bird catches the worm", "Infancy, when Wordsworth had 5 across of 5 down", "Premature", "Advanced", "In good time", "Immature" and "Before the ETA".)