I have 3 years to complete my BS (GI Bill chp 33). 3 semesters in, and I have already completed every general ed course, I suppose you could say that I have the equivalent of a general AS/AA now. Taking so many heavy-writing based humanaties courses at one time was a huge pain (at least getting A's in all of them anyway). I have 9 more semesters in which to finish a Physics BS, with absolutely no room for time off. The only issue that I think might hurt me is that many of the upper level physics classes have sequential pre-requisites. I still have to complete CalculusI/II/III, PhysicsI/II/III, and DEQ which many of the other courses I need to take require. In my case, the "take a whole bunch of classes at once" approach won't really work out to well.
I think that I might come a semester or two short of my 3 year mark (for funding), but I hope that financial aid will cover the remaining courses I might need. I think that if you don't have to work, and have a really good work-ethic, you might be able to do something like this.
Though, realistically it all comes down to planning your schedule very carefully.