End of day fixed: around noon in America (6)
I believe the answer is:
sunset
'end of day' is the definition.
(I've seen this before)
'fixed around noon in america' is the wordplay.
'fixed' becomes 'set' ('set' can be a synonym of 'fixed').
'around' indicates putting letters inside.
'noon in america' becomes 'uns' (I am not sure about this - if you are sure you should believe this answer much more).
'set' enclosing 'uns' is 'SUNSET'.
Can you help me to learn more?
(Other definitions for sunset that I've seen before include "End of the day, getting dark" , "After which day becomes night" , "US nest (anag.)" , "Onset of night" , "Final declining phase (of something)" .)