Assuming that it will be slower and more difficult to get things done after around 15 December, this should be the final date by which everything is done. You cannot apply for bankruptcy travel permission until you are actually bankrupt and this process typically takes about two weeks. To be safe, you should allow three weeks as it is a busy time of year. Ideally you would apply for travel permission earlier, and before buying tickets. If we assume that you need to apply for travel permission by three weeks prior to 15 December this gives us a date of 24 November.
You then need to allow time to draft your bankruptcy application (between one day and around two weeks, in most circumstances), and for the Official Assignee to process your application and make the bankruptcy order (usually 2-3 weeks). Taking 5 weeks to be safe, the bankruptcy process should begin in earnest before 20 October if you want to have a trouble free visit to New Zealand. Ideally you would start the process now so that there is plenty of time and you know that everything is sorted before buying tickets.
If you need assistance to get matters resolved we can help. At the moment we have some special packages available. Please ask if this is of interest