He's not free, yet may have time (7)
I believe the answer is:
convict
'he's' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'not free yet may have time' is the wordplay.
'not' becomes 'con' (I've seen this in other clues).
'free yet' becomes 'vic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'may have' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'con'+'vic'+'t'='CONVICT'
Can you help me to learn more?
(Other definitions for convict that I've seen before include "Imprisoned criminal" , "One serving time" , "Prove guilty" , "Jailbird" , "One in prison" .)