I recently attended phases 2 & 3 at CTC Dibden Manor.... Unless you live near to there I'd plan on staying in a B&B/Hotel in the area as they expect you to be on site for a prompt 8.15 start.
You then have a presentation for approx 1 hour... then a Q&A session.. then 15 minute 15 maths q. test and then PILAPT. Approx 1 hour.
After that you have a break and then have a group exercise. It's all about how you communicate within a team, there are no exact right or wrong answers, it's all about your ability to listen, decide, review, lead, etc...
I was offered a place after selection, and I can't suggest a better book to buy for prep other than 'get a head for the sky' .... google it. pay £15, read it, cover to cover, over and over again.. and you'll get through
The only other thing to mention is be aware that you're under scrutiny from the second you walk in.... be friendly, use peoples names when speaking to them & be smart.