To get the validation permit you have to do what basically amounts to a New Zealand BFR, so it can be done relatively easily in one flight especially if you are in current practice, but it is a bit more than the usual few circuits that would be required for a "check flight" if you were just looking at hiring an aeroplane from a different operator to who you normally fly with in your home country.
The TTMRA, as far as I understand it, just means that Aussie CPLs don't have to jump through the usual hoops that are involved in converting an overseas CPL to a NZ one (e.g. a requirement to actually do a CPL flight test, have 10 hours of mountain flying training etc.)
I'm not a local to that part of the country but the couple of times I have flown in there really served to emphasise how it could catch you out - two or three hours difference on a day where the conditions at Queenstown are completely stable all day can turn MF from a beautiful calm airfield into a washing machine that has you questioning how tightly the wings are bolted on. Not to mention, if you get a nice day, you can expect to encounter a very large number of GA aeroplanes and helicopters operating in what amounts to a pretty confined space; the mandatory briefing prior to flying in there is to protect against mid air collisions as much as it is to protect against people burying themselves in the side of a mountain.
My advice would be don't bother trying to do it solo - take an instructor and then above all else you can concentrate on enjoying the scenery!