How long can I stay in Australia on an eVisitor (subclass 651)?

The eVisitor is a multiple-entry visitor visa valid for 12 months from the date it is granted.

During that period you can enter Australia as many times as you like, and you can stay for up to 3 months on each visit.

It is intended for short-term travel, so it is not suitable if you need to stay for longer than 3 months at a time. For longer stays, another visitor visa may be more appropriate.