You can book your theory test as soon as you have your provisional licence (though you'll obviously need to revise for it!).
Once you've passed you have up to two years to pass the practical test. We obviously don't advise you take your theory unless you are
planning on learning to drive fairly soon after.
Because of local waiting times practical tests need to be booked several months in advance to secure a preferred time. Your instructor
will let you know when the appropriate time to book. Don't worry if you're not ready for your chosen test date you can defer it up to
three days before the booked date without losing your fee.