Hi,
Let's look at each of your q's...
1. Re: one-year MBA programs for career changing... in GENERAL, I advise that if you are making a career change, particularly a drastic one, a 2-year program is better suited, as you have more time to explore options, take on more classes in particular areas of need, and of course complete the summer internship that can help greatly in your new area. However, that being said, many many students still use one-year MBA programs to change careers successfully, so it is possible. It depends a lot on what the change is and how it makes sense and what sort of experiences from the past may be relevant to the future career. Also in many of the one-year programs you CAN still complete a summer internship. If staying in same function but changing industry, it may be a bit less difficult as well.
2. Last I was aware of, LBS, Said & Judge used rounds of admission (in fact I know Judge and LBS have 4, vs many US schools with 3). Of course you should reference each school's website for deadlines for this coming year! LBS can be completed in 15, 18, or 21 months. Judge and Said are one-year programs. In terms of actual intake dates I do not know of more than one intake/start date at the 3 UK programs you asked about.
3. For your question about ranking and Said/Judge over some of the US programs, it really depends on what region of the world you want to work in and what career/industry... at some top finance or consulting firms, specific brands of MBA may be more appealing or give a bit more of a plus on your resume... but at many other management roles at a large variety of firms/companies, it is more about having a well-known program... if you are in the US, the US schools may have more of a bump... if you are in Europe, while top-10 US schools will still be best-known, once you get beyond that some US schools won't have the brand recognition abroad. Oxford and Cambridge of course have global recognition which says a lot (more than 'University of Virginia'), but again it depends on where you want to work and what you want to do.
4. You should apply when you have the best application you can put together.... earlier is generally better just because there are more places available in the program.
Hope that helps!
Jen