Not sure how it's working now, but when i went through CTC, you did the ATPL distance learning course where you read the manuals in your own time, and then submitted online progress tests to BGS. Most of the groups tend to head back after about 5-6 months for the first set of exams - basically usually a week off, followed by a week 'brush up' course at BGS (who admittedly are AWESOME), followed by another week off, then a week of exams at your chosen CAA exam venue.
The date for the second set of exams is a little more flexible, just depending on when you finish the training syallabus in NZ, but the admin staff at CTC organise the bookings of the exams accordingly. Whether it's still the same now i'm not sure, but that's how it was up to the end of 2005.