Welcome from a fellow Kiwi - love that area of the country. It should be a great ride - nearly all down hill and relatively flat, however keep in mind the short winter days make it difficult sticking to training schedules......
Between now an November you have heaps of time to get fit enough for the event. It's 160km for the full event - more than big enough to be a challenge - 9 hours is a pretty generous cut off time, - especially given the 600 vertical meter overall descent. The top riders are finishing around 4 hours, so if you can make half their speed you still have time up your sleeve.
If I was in your shoes, I would start by pushing your training time out (preferably on the road, but wind trainer is OK to start with), until you can do 1 hour comfortable. I would use a heart rate monitor if doing indoor training to keep me honest. Outdoor I find it useful but not essential.
I would drop to no more than 3 days a week (With 1 day between - never back to back days). Once you have comfortably gone an hour, something like
Day 1 - Long ride - 5-10% longer each week, slower than race pace
Day 3 - Medium ride - 70-80% of above, slower than race pace
Day 5 - 30% of above at faster than race pace / sprints / interval training.
Optional - Only if feeling good and drop the instant you have any symptoms of over training
Day 2 - Nothing.
Day 4 - Very slow, easy ride.
Day 6 - Very slow, easy ride
Day 7 - Very fast, short ride or sprints- no more than 1/2 hour - ONLY of feeling really good.
The one key ride is the Day 1 - long slow distance. I would aim to be getting it to 140km about 3-4 weeks out from event. If you (honestly) aren't feeling up to it, don't train - over training is your worst enemy. You will drop training rides - it's OK. If you have more than 2 weeks layoff, then you will need to go back a few weeks and built up from there, otherwise, it won't hurt to miss a few, and will do more harm than good if you try to "make up" for it.
There is lots of plans an information out there - read up on a couple and cherry pick what suits you. Be very aware there is a lot of pop-science behind many of these "plans" - base on extrapolating the results seeing a .0001% performance improvement in an elite athlete and then applying that to "You will go faster if you......." Essentially read up on our own Arthur Lydiard - his work in the 60's is the foundation of most training schedules today.
It's essential to build endurance, then build speed.....