You can get used to it. In college, I had a semester where I was taking 6 classes, half of them project heavy grad classes. I only pulled one all nighter (that was on me) that semester, but I was regularly getting 5-6h of sleep when it wasn't Friday or Saturday. After a few weeks, it wasn't that bad until spring break came around. I got used to getting 8h again, so I had to readapt back to 6h.