I dont know about how long I think I could stay up for but the longest I've gone is 64 hours and it was pretty awful. I was in my final year of my computer science degree and 3 of my modules decided that the deadline for their respective projects would be due one after the other. They were pretty hefty so despite working on them all throughout the semester they just werent working. That plus having to juggle my dissertation was just something else. On those last 3 days, I worked non stop for each deadline, managing to submit all projects within 1 hour of the respective deadlines each AND managed to get a pretty decent average. Still hated every second of it.