My billing due date is in the next 3 days and I signed up for preauthorized debit payment from my chequing account yesterday, will I get charged for a late payment? (as i dunno whether or not it'll get effective in the next 3 days)
It usually takes a few business days. I think that you're usually advised to give a 5 (business?) day margin of safety just in case. You generally aren`t charged a late fee if it just comes in a couple days late.
Preauthorized payments generally take one full billing cycle to take effect. i.e. If you set it up after you receive this months bill it will be effective in time to pay next months bill. You will need to make a manual payment for this months bill.