I phoned and alas you're right.....I wanted to activate this from my stay at POP - but they won't let me.
To change it would mean having to try and get an extra night at the start to take AKL to 5 nights, either change/cancel our night at Universal and then maybe change from 12 to 11 at POP - more hassle than it appears to be worth.
It's a shame there is no way of sorting this out.....