Artist turning up two hours before noon (5)
I believe the answer is:
manet
'artist' is the definition.
(I've seen this before)
'turning up two hours before noon' is the wordplay.
'turning up' says the letters should be written in reverse.
'two hours before noon' becomes 'ten am' (I've seen this in another clue).
'tenam' reversed gives 'MANET'.
(Other definitions for manet that I've seen before include "Painter of Le Dejeuner sur l'herbe, d. 1883" , "French painter" , "artistic individual" , "Olympia painter" , "Edouard ---, pre-impressionist" .)