Tokyo is incredibly popular at the moment especially in Business Class.

For both ways I would call at 0050 to the Australian number (you will need a suitable app), and try and do on the phone. If you can’t get through in time or you get through early and the agent won’t wait then I would in parallel have computer open to try online at 0100.

You may have to suck up a phone booking fee or two but it is probably worth it to get what you want.

Make sure in advance you have all travellers and credit card set up on the BA profile to minimise data entry.

Ultimately phone agents can hold seats in an instance, so online will always fail if someone has got there first on the phone.