Bright composer, finishing early, to return before noon (6)
I believe the answer is:
agleam
'bright' is the definition.
('agleam' can be similar in meaning to 'bright')
'to return before noon' is the wordplay.
'to' becomes 'elga' (I can't explain this - if you can you should believe this answer much more).
'return' says the letters should be written in reverse.
'before noon' becomes 'am'.
'elga' reversed gives 'agle'.
'agle'+'am'='AGLEAM'
'composer finishing early' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for agleam that I've seen before include "Bright" , "Sparkling" , "scintillating" , "Shining brightly" .)