Basically, when you pay a cheque into your account it will immediately show as a credit, But it will still take the same cheque processing time which is between 3-5 days to clear as 'available funds'.
The cheque is presented to the drawers (person who wrote the cheque) bank account to debit, and those funds are then credited to your account hence the time frame. Try internet banking, a lot quicker and most of the time immediatley credits other accounts.
If you have an overdraft limit and you are still within this limit when
your payments debit from your account, they should still go through ok however, this depends on how your risky the bank feels your account is in general. You may be charged a higher interest rate for your bills/payments until the cheque you paid in, is fully cleareed into your account.
I hope this makes sense