If you want to book in advance in order to fly on a particular date and time, pick a different airline.

I booked in July to fly return from Osaka to Wellington just before Christmas, which involves one international booking to Auckland (going via Gold Coast) and then a connecting domestic flight booked separately but also with Jetstar to Wellington.

At first it seemed fine. Then two weeks later I got a call from a representative telling me that my flights had been canceled. Because I could afford to depart and return a day earlier that was resolved painlessly, and the staff member was helpful. It also meant changing the booking of accommodation, but luckily that also worked out ok.

But yesterday, several months later, I received an email telling me my domestic flight had been changed, leaving me only 30 minutes to transfer from International to Domestic terminals in Auckland, an impossible task. When I call up to sort this out I was kept waiting by the skype call center for over half an hour, listening to their irritating advertisements the entire time, and then spent 45 minutes after that speaking to a customer service rep. Incidentally, it turns out that the second leg of my International flight had been changed without any notification to me, extending my layover in Gold Coast from 4 hours to 16 hours. This in turn meant that I would have missed my connecting flight to Wellington, which I wouldn't have even known about if they hadn't screwed me by changed the time of that flight in the first place.

The poor customer service rep was left trying to find some less appalling flights to put me on, but couldn't do so without me having to rearrange holidays for both me and my GF. In the end the best we can do is to endure a 16 hour layover in the Gold Coast, then arrive at Auckland just in time to spend the night at the airport and fly out in the morning, for a total of 22 hours of waiting in Airports when I was originally booked to have only 5 hours. They offered to refund my money, but at this late date organising flights with another airline would be prohibitively expensive, if even possible at all.

End tally - Flight times and dates changed on me three times (and counting) since I booked, only two of which I was even informed about.

Moral of the story - If you want to organize a trip and be able to rely on your airline for dates and times, Jetstar is not the one for you. If you've got an open window of a few days on either side and don't mind putting up with the hassle and stress of multiple hours of negotiations and phone calls/being on hold in order to reconfirm details, then by all means, be my guest. What you save on money with Jetstar is certainly paid back with stress and time.

International
Japan-Osaka (Kansai International)
New Zealand-Wellington