When I did my masters degree, I applied in September 2005 for courses starting in September 2006. I got acceptance letters around December/Jan 2006, and I either accepted or declined the places just after that.
After accepting a place at Leeds, I had a funding interview in March - I already had a place on the course, but they were just interviewing everyone to see who they were going to give grants/extra funding to (I didn't get any funding though).
In June I changed my mind about going to Leeds, so I called the department at Bristol Uni and asked if I could still join their course instead (I had previously asked if they could keep my place open, as the Leeds course was dependent on enough students enrolling). They said yes, and I went for an informal interview to look around the place and find out more about the course. I accepted the Bristol place (and turned down Leeds) at the end of June 2006 and then started the Bristol course at the beginning of October.
In terms of fees, I thought the stipulation was that if you will have been in the UK for 3 years (and hold ILR) by the start date of your course (presumably September), you can qualify for home fees. If not, then you have to pay international fees. So, I would imagine that they might take this into consideration when calculating your fees.
I'm not sure if this is correct, but I thought that your fees applied throughout your course... so if you are on international fees to start with, you can't switch to home fees halfway through (even if you meet the 3 years partway through, you still have to continue on with international fees) - I don't know if that's right or not though.