Being tired, not keen about a late finish (5)
I believe the answer is:
weary
'being tired' is the definition.
('weary' can be similar in meaning to 'tired')
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for weary that I've seen before include "Whacked" , "Tired - bored" , "Ready to drop" , "Enervated" , "Physically and mentally fatigued" .)