I asked much the same as this a little while ago and noone responded, so curious myself.
The ATO website has things like your electoral roll registration is there, your personal possessions are there and a few other things and some other rather vague waffle. We've already got the utilities connected there and all sorts of weird stuff like towels, a kettle, various cutlery and crockery, spare cot, bed, chairs etc there ... the council was about to ping us for living in such squalor (the house has no kitchen and has several floors in varying degrees of being ripped out and replaced) but were happy that we had a primary residence elsewhere and were only staying there a day a week tops.
We were planning to properly move into ours for most (if not all) of next year just to be doubly sure, but we will be seeing an accountant to work out the best options once we've finished the reno. Our case is for CGT not FHOG though, and our biggest problem is simply that the other house is *much* smaller than ours, or we'd just move into it permanently and sell my old one.