The bristol cd rom contains all the course material, so you can do it via that, or the text which you are also supplied with. As stated, the cd rom does have animations and a bank of progress tests that you do, then uplink the results to the school via the interwebthingy. You do get your results immediately.
I also used the oxford weather cd, it's very good, but as it contains the whole met course, you may not have time to do it twice.
There is no time limit other than that imposed by the caa from the time you take your first exam to the last. You study at your own pace, then when you think you may be ready for the revision course you book that, I would plan that a couple of months in advance. Also book accomodation well in advance, the closest ones to the school get booked out very quickly.
The website is very good for having questions answered. The instructors are quick to respond, and usually plenty of students too.
Best of luck with your decision.