Technically I believe they are supposed to aknowledge the...

Technically I believe they are supposed to aknowledge the payment as being made same day?  I would think you could BPay it today if you wish (before cutoff).

When does the biller receive my BPAY payment?

If your payment is made on a bank business day before 6pm (Sydney / Melbourne time) it will be debited from your account instantly and processed that day. The biller will acknowledge the payment as having been made that day and should process the payment the next banking business day.

If you make a payment on a weekend or public holiday, or after 6pm (Sydney / Melbourne time) Monday to Friday, the payment will be debited from your account instantly and processed the next business day. The biller will acknowledge the payment as having been made on the next banking business day (this does not include weekends or public holidays).