At BYU I was at school from 8 to midnight, with few exceptions. At Berkeley, I typically arrived on campus around 10 am and left around 4 pm.

Folks were really laid back. My specific program had our own library, and most of grad students stayed there and goofed around most of the day. Most of the PhD students are likely still "2 or 3 years away" from graduation, five years later. This was at the #1 ranked graduate program in my field.