Not sure on the current delays between applying and ground school but being delayed at that stage is probably the most convenient as you can keep your job etc. and work until it starts. As a white tail you're almost definitely going to be delayed at least 2 months between ground school and basic flying stage. There are some courses that have been delayed as much as 6 months between ground school and flying. I'm not too sure about delays between basic and advanced flying stage, it seems as though these have been kept relatively minimal - probably as you're correct that they are sending some of their cadet to Leading Edge for parts of training.
When it comes to being booked in for flights the priority are the airline funded cadets (Royal Brunei, Hong Kong Airlines, Cathay, Oman Air, Air France), followed by tagged cadets (easyJet, BA, Wizzair) and then white tail cadets, this combined with weather (especially in New Zealand and the UK) means that at times as a white tail you're only going to fly once a week or once every two weeks.