In mathematics, bang is used as a term for factorial, which is also represented by an exclamation mark (!). It’s in Collins, which is the Times’ source of reference, rather than the BRB. So it’s obscure, but ok.
6 Down What bit possibly can be over by Thursday? (5) T*O*H
I am still bemused by this one. The solution has to be TOOTH (as noted by puzzledbob) or TROTH. ORT is defined as bit so the clue may be &LIT but I'm not convinced. Any suggestions girls and boys?