Diminutive member of the staff on watch (6,4)
I believe the answer is:
minute hand
'the staff on watch' is the definition.
I can't judge whether this defines the answer.
'diminutive member' is the wordplay.
'diminutive' becomes 'minute' (I can't explain this - if you can you should believe this answer much more).
'member' becomes 'hand' (hand is a kind of member).
'minute'+'hand'='MINUTE-HAND'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for minute hand that I've seen before include "Bit of a watch" , "A pointer" , "Part of watch or clock" , "that Mimi had" , "is on time" .)