I know that feeling, I did the same thing last year and am now regretting it. I logged onto student finance today to start my application and it said in big bold letters "1 MAY 2012", which turns out to be the deadline for the whole thing, including all of your evidence and the time it takes them to ask for it. You can still do it later than that but you won't get your first loan installment in time for the start of your course.
The form has been pretty straightforward thus far, but it took me an embarrassingly long time to work out my course finish date!