Single chap comes in punctually (6)
I believe the answer is:
ontime
'punctually' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'single chap comes in' is the wordplay.
'single' becomes 'one' (a single thing - only one).
'chap' becomes 'tim' (short for Timothy).
'comes in' is an insertion indicator.
'one' enclosing 'tim' is 'ONTIME'.
Can you help me to learn more?
(Other definitions for ontime that I've seen before include "Prompt" , "Sharp" .)