It's unregistered, but your registration is not cancelled immediately. There's a window where you can pay it late (but not drive it) without needing to get a new RWC
in Vic, it's three months from memory. our regos are due within 2 weeks of each other - we tend to take one car off the road for a month or so and register it later each year (off setting it by six months puts it due between christmas and new year - not a good time!)