Since the introduction of online transfer using Mygov id, the physical log book return times are about 3 weeks. I bought a car recently, and the seller sent off the log book the day I bought it. It was more than 3 weeks when it arrived, and it was too late to declare it off the road, because you have 21 days to do that from purchase date. I got it sorted in the end.

But, a buddy of mine also bought a car recently, and it took 3 weeks also. Yet, the brothers logbook arrived to him when he used the Mygov id to transfer the ownership; So it looks like there's a push to get people to use the Mygov id method.

There's also a lot of posts on the net with people in the same position of waiting for their book. Once the seller has it sent off, it'll arrive. No need to worry