Serve, late in the evening, first of diners (6)
I believe the answer is:
attend
'serve' is the definition.
(I know that serve can be written as attend)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for attend that I've seen before include "Be present or appear at" , "put in an appearance" , "Go regularly to, church perhaps" , "Completed" , "Show up" .)