What happens if I've set an online transaction or planned payment for today and it's a weekend or national public holiday?

All Bill Payments to another Westpac account will occur immediately - 365 days a year.

If it's a national public holiday or a weekend, the transaction will still be deducted from your account, and processed to the recipient's account on the same day so long as you have enough funds in your account.

For Automatic Payments:

 If the scheduled payment date falls on a weekend or a public holiday then it'll still be processed on that day in accordance with your instruction when setting up the Automatic Payment.

See here for more information regarding payments made to credit cards.