A little hard to say. When I was a grad student and classes were done, my time was divided between lab work, writing (my desk was in the lab...no escaping to an office full of students to keep me entertained), TAing (in my last years, I was the head TA, so was also chained to a pager for the other 20 TAs to be able to reach me if there was an emergency and they needed help finding someone to cover their section), and coordinating activities in a dorm for students in math, science and engineering majors.
My schedules would go something like: Mondays 8 AM to 10 PM teach 3 3-hr biology labs, and hold an hour of office hours, and run out to the farm for a half hour to give injections for my experiments between classes I was teaching; Tuesday get out to the farm at 2 AM to start experiments, take an hour break for breakfast, finish up the experiment about noon, run all my samples back to the lab, take an hour for lunch and nap, head to the lab to process my samples and start setting up assays, then back to the dorm to read, write, and counsel undergraduate students until the wee hours of the morning. Wednesday get to the lab around 10 AM, set up assays all day, go back to the dorm, run a peer study group in biology after dinner, go back to my room and work on reading and writing. Thursdays, same lab schedule, but after dinner, do a 3 hour prep session for the next week's biology labs, then head out for drinks and socializing with the other TAs. Fridays, more lab work all day, go out for lunch with the grad students in my dept., attend the afternoon seminar, attend the reception for the seminar speaker (free beer and pizza!...this was before public universities started prohibiting alcohol in academic buildings), work late in the lab because the dorms would be noisy and I hadn't gotten anything done all afternoon, email my boyfriend lamenting that it was another Friday night that I was working in the lab instead of seeing him, get back to the dorm, find all the notes from students about all heck breaking loose on a Friday night...who was at health services, who was in the hospital, who was seen getting picked up by her parents in a fit of tears, who broke up with whose boyfriend, etc. Saturday and Sunday, sleep in until noon, head to the lab, work until 10 PM or so, get everything set up for the following week's experiments. I left out that somewhere in there I was holding about an hour or two of office hours a week in the dorm as a mentor/academic advisor/mother/psychologist to the students there, plus some weeks we had guest lecturers or other events to arrange. During exam weeks, the grad students in the dorm took turns running the study breaks (basically making sure there was plenty of snack food out). I coordinated all the programs run in the dorm for two years (keeping track of who was inviting what speakers, running the budget, keeping attendance of which students attended...they had to attend a minimum number of activities to be permitted to reapply for that dorm the following year...making sure the speakers arrived and were properly greeted, etc.)
I think I slept some, but I don't remember doing much of it. The most relaxing time I had was preparing for my qualifying exams (I had a whole month when nobody expected me to be anywhere but studying...it was sheer bliss!) and writing my dissertation...again, nobody expected me to be anywhere for a couple months except in front of my computer at home writing. I even had time to go to the gym an hour every day.
Most grad students aren't QUITE as masochistic as I was though, and don't usually take on that many extra responsibilities outside of research and possibly required teaching. I actually enjoyed doing all those other things though...living in dorms as a grad student did wear thin after a while, but I was able to squirrel away my stipend and have some savings for a downpayment on a house by the time I was done with my post-doc. For me, the short term sacrifices were worth the long term benefits (with all that I was doing, I still got done with my PhD in 4 1/2 years without doing a masters first...having a variety of things to keep me busy kept me from getting bored or lazy).
All I remind students is that the longer hours they put in getting work done, the more they accomplish and the sooner they get out. Some people would prefer to work long hours and get done sooner, others would prefer to leave more time for going out with boyfriends/girlfriends/other friends on evenings and weekends and take a bit more time to get done with their degree.