It'll be the constant sleep debt built up over the semester that'll get to you, so say over 9 weeks (12 weeks semester, there is a 'mid'-sem break where the 'middle' of the 12 week semester is after week 9, (although it's supposively the middle of the 12 weeks+exams, but then first sem doesn't run it like that...).. anyways). So yeah as low as 5 hours a night (sometimes lower), and then add in the all-nighters that you might have to pull even if you have kept up with the course, to actually get assessments submitted on time. You might be able to run at max for a little while doing this, but over the course of the semester (and swotvac... swotvac can be painful) it takes it's toll.
It's probably a little easier in first year, I was pretty drained but had 3-4 hours of travel time each day. Second year it steps up a few notches, and even living 10 minutes away from uni I was still pushing it on sleep and rest.
I should note not all uni students do this, but most of those who do well in the end seem to. Uni is another whole step up from VCE, VCE seems so easygoing relative to uni (although as the others have said you get long as holidays).
EDIT: If anything, just look back at posts from first years on here from a little while ago, you'll see the difference compared to VCE.