It really depends on the degree you are doing. From experience, you wouldn't want to stack engineering classes, especially labs (which go for 3 hours) as they are pretty intense, and therefore tiring. You don't want to turn up to a lab tired as its when you do most of your learning. I've been lucky enough not to have labs back to back, but even after one lab, you get pretty tired. I assume biomed lectures and labs are similar. Also, breaks are great for catching up with friends or just grabbing lunch.
However, in the case of commerce, which is less hands on than engineering, I could probably stack 3 or 4 lectures in a row and be fine.
On the topic of minimising your time on campus, it may depend on if you are going to attend all your lectures. Last semester I had only one lecture on Fridays, and I initially planned on staying home and watching it, but I actually ended up spending half a day or more at uni for engineering group work, so my planned 4 days effectively became 5.
If you have any engineering specific questions for me, please PM or ask here.
- Orson