I seem to on a scheduling kick in my recent posts, but I just read Isis' post about working hours for grad students and it reminded me of my own experiences.
My grad advisor was extremely laid-back. I pretty much ran the show for my thesis project, independently checking in once or twice a week when he was around and going without when he was traveling (about 25 percent of the time). Needless to say, he didn't dictate working hours.
Then again, unlike Isis, my research focus was fieldwork, not labwork. And most of my fieldwork was solitary - a single helper if I was lucky. So my advisor didn't really expect me to be around all the time.
When I was not actively doing fieldwork, I tended to have a pretty set schedule. I'm a morning person and my natural schedule is to sleep from 11-7. So I was one of the first grad students to arrive in the morning (around 7:30), and I would screw around online/get distracted by my friends during the day, and work until 5 or so. I would end up working in my office at school about every other weekend, rewarding myself with takeout for lunch from one of the multitude of cheap restaurants within walking distance.
I miss that schedule. I didn't have a sweetie distracting me, and I lived a 15-minute walk (or a 3 minute drive, if I wanted to illegally park) from my office, and it felt like I had all the time in the world. Now, I spend 2 hours driving to/from work (if I'm working from the office) and we have the tremendous time-suck that is cable, and my sweetie likes having actual dinner, and so the time available for myself just keeps shrinking.