With the new kinder hours, 4yr kinder is for 15 hours / week. which means that a single kinder teacher can't take 2x4yr classes.
We have just found out that this is not compulsory. Our kinder is offering 2 x 15 hour groups and 1 x 10.45 group for the 4yo.

In our area 3 yo is run by the kinder itself, 4 yo is run by the council. You can enrol in 3yo whenever you like - but no earlier than 24 months. 4 year old kinder enrolment for next year closes in a week. So it's not super crazy down here. You don't have to enrol the day they are born

PZ. It's good that you question the necessity of it. As with all things with your DD, you are making your own decisions based on what is right for you and your family.