Brat hasn't time to make mistake (5)
I believe the answer is:
Here is my best explanation:
'mistake' is the definition.
('error' can be a synonym of 'mistake')
'brat hasn't time' is the wordplay.
'brat' becomes 'terror' ('terror' can be a synonym of 'brat').
'hasn't' suggests deleting specific letters.
'time' becomes 't'.
'terror' with 't' taken away is 'ERROR'.
'to make' is the link.
(Other definitions for error that I've seen before include "Faulty judgment", "Slip-up", "Fallacy, mistake", "Bug", "Slip, blunder", "Fault", "Wrongdoing", "Inaccuracy", "boob" and "miscarriage".)