I'm not defending this crappy inflexible system but here are a couple of top tips to help anyone who needs them:
1. If you're wait listed for an FOC you need to be at the airport 2 hours before so they can transfer your data across so you keep your priority - I saw it in the FAQs somewhere.
2. If you're being caught out by the 4 hour rule you can book for a flight the next day so that there's a ticket in the system that they can find and move onto the flight you want.