Bit of sunshine right before a day’s end (3)
I believe the answer is:
ray
'bit of sunshine' is the definition.
(a ray of light)
'right before a day's end' is the wordplay.
'right' becomes 'r' (common abbreviation).
'before' means one lot of letters go next to another.
'end' says to take the final letters.
The final letter of 'day' is 'y'.
'r'+'a'+'y'='RAY'
(Other definitions for ray that I've seen before include "Sunbeam or flat fish" , "Man, maybe" , "Gleam" , "Shaft of light" , "Beam of light or flat fish" .)