You can start revising for your theory now, but only sit it if you feel ready to. Otherwise you're chucking £23 down the drain. Don't do it quickly just so you can pass quickly.
8 hours a day is a lot, and driving lessons are hard to get - my instructor isn't taking any new students on until September. Getting a test slot will be hard as well, I have mates who have been waiting months to get a test.