I disagree about the 3 months, I applied in late April of 2004, (April 28th I think, I still have my copies of everything at home) - got approved a few short weeks later, and got approved and my documents returned at some point in May.
I requested to have my visa good from July 6 2004 to July 6 2005 due to wanting to travel and settle into Bristol for the summer months, and it was approved from July 1 2004 to Oct 31 2005.
Uni started the last week in September 2004.
I ended up arriving in the UK on July 6th 2004, and leaving July 21 2005.
As long as you have the paperwork from your uni, you should be able to apply more than 3 months ahead, I had no problems with mine!
It might help to see if your uni has an international students office, they might be able to speed the process up, though all I THINK I needed was the acceptance letter from my uni stating that I was accepted, my dates of study, and the tuition/fees I'd have to pay. Other than that it was bank stuff and the application I beleive.
if you want, I'll list out what I still have copies of at home, I beleive it's everything except the application form (did that online) - but i'll need to double-check.
I hope this helps!