It may hurt a little at closing time (4)
I believe the answer is:
bite
'it may hurt a' is the definition.
The definition suggests a singular noun which matches the answer.
'little at closing time' is the wordplay.
'little' becomes 'bit' (a small bit).
'at' says to put letters next to each other.
'closing time' becomes 'e' (I can't explain this - if you can you should give a lot more credence to this answer).
'bit'+'e'='BITE'
Can you help me to learn more?
(Other definitions for bite that I've seen before include "Quick snack" , "Get teeth into" , "champ" , "Small amount of food" , "Grip; take effect" .)