Disappear round middle of afternoon in coat (7)
I believe the answer is:
varnish
'coat' is the definition.
(varnishing is a kind of coating)
'disappear round middle of afternoon' is the wordplay.
'disappear' becomes 'vanish' ('vanish' can be a synonym of 'disappear').
'round' indicates putting letters inside.
'middle of' says to take the centre.
The middle of 'afternoon' is 'r'.
'vanish' enclosing 'r' is 'VARNISH'.
'in' acts as a link.
(Other definitions for varnish that I've seen before include "Wood or nail coating" , "Transparent resin coating" , "Apply hard shiny top coating" , "Glossy stain" , "put on coat" .)