Zeon: Yea cheques take a while to process and a while to deliver. More than 5 business days for the whole process. Payment terms of at least 14 days is reasonable IMO?
Yes, if Slingshot agree to accept a cheque as a valid form of payment (and most telcos still do) then they need to allow a reasonable amount of time for that type of payment to process.
I know with Telecom the due date is approx 14 days from the invoice date which is reasonable. They don't send any notices until the account is at least one month overdue - The late payment fee is incurred if you haven't paid by the time they print the next months invoice - not the day after the due date.