Calling time, Harry locks up (6)
I believe the answer is:
naming
'calling' is the definition.
('name' can be a synonym of 'call')
'time harry locks up' is the wordplay.
I cannot quite understand how this works, but
'time' could be 'min' and 'min' is found within the answer.
'harry' could be 'nag' ('harry' can mean 'to persistently bother') and 'nag' is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for naming that I've seen before include "Calling" , "Allotting term to" , "Christening" , "Identifying, citing" , "Identifying; mentioning" .)