Any time I've got a bank draft the money was taken out of my account, so effectively I was walking around with cash. I assume if the draft is drawn on a different bank and paid into another bank like you say, the clearing will take a bit longer.
I didn't know you could cancel a bank draft as easy as that, so does that mean one could sell their car on a Friday evening, accept a bank draft as payment and then on the monday discover the draft has been cancelled?