Day in the life of a science PhD student?

No, not even close. You'll have some stretches where you'll top 80 easily, but for the vast majority of your five or six years, you're doing maybe 20.

It's highly variable depending on your project and your adviser. Especially in biology, where your experiment might depend on the growth rate of some particular organism. For example, if you have 2 hours of prep time, then treat the cells you're studying with a drug, and examine the effects of the drug after 12 hours, then it's obviously going to be a long day. And some organisms need to be maintained on a set schedule, making weekend work sometimes unavoidable. But days when you're just reading (or writing) papers or analyzing data can usually be as short of long as you want them. I just finished my PhD in biochemistry, and I probably averaged around 60 hours a week overall, with a range of maybe 40 - 80.

All that said, though, there's probably no way to know without talking to people in the specific program you're applying to, and then the specific lab that you're interested in. I wouldn't write off grad school because of the hours, but try to get a sense of the department culture when you do interviews.

I have a few close friends that are getting their PhDs, some in science and some in humanities. This includes ex/current roommates and girlfriends (i.e. people I spend a lot of time with). In general, graduate students LOVE to whine about the hours they work. There are plenty of people that work for salary that work as much as grad students. When a grad student says they work 80+ hour weeks, ask them to actually break down their weekly schedule. Working a real 80 hour week involves going in 7 days a week and working for 11-12 hours. That doesn't mean you go in at 7, take a two hour lunch to eat and run, and then leave at 7. That is not a 12 hour work day. While I bet you CAN find some grad students that work 80 hours a week on a consistent basis, that is NOT the norm. Another thing: those with "normal" jobs generally have somewhat stable hours, so when they quote hours worked per week that is a typical week. Grad student hours vary a lot, so while most have probably worked some 80 hours weeks, they do not do this consistenly. Many like to quote their highest work week as opposed to their average.

That being said, credit where credit is due, grad students do work a fair amount. I would say 60 hours a week ON AVERAGE is what many successful students at top programs put in. The big thing with being a student is you get to choose your OWN hours. When you work for a company, your time is not your own. I think grad students that do not work a job after undergrad do not understand this. Had a late night last night? Go in late the next morning. Want to take off at 3 in the afternoon for a long run? Go ahead. You can make that up over the weekend or in the evening. You just don't have that flexibility at a desk job. On the flip side, I have a friend that is a biologist and sometimes with his experiments he has to be at the lab for 15 hours stretches. While these days are few and far between, they still suck. You also have more flexibility with vacation. Things are generally slow in the summer and students take long vacations (not like undergrad, but long compared to those working in an office). It is also easy to take long weekends around holidays. Try explaining the concept of PTO to a PhD student.

The last thing I can say is, if you don't really like what your studying or your time management skills suck, don't be a grad student. At a desk job, it is pretty easy to coast through 40-50 hour weeks. It is much harder to motivate yourself to do 60 hours if your heart isn't in it. It is easy to get stuck in a rut while working at an office, but at least you are still taking home paychecks. If your studies start to stagnate, you are really in a bad place. You can either leave your program with nothing to show for your efforts, or you can try to work long hours to get a degree that you probably don't even want any more.

I'll add that I'm a working stiff with a desk job.

A agree with the above poster. It is highly variable depending on program, adviser, project and experimental system. However the biggest variable is you. Like running or undergrad a PhD is what you put into it. You have to decide what you want to get out of yout PhD and work accordingly. I am in my 5th year in a good program (virology). I am trying to peruse an academic career and on average I work at least 6 days a week and 55-60h. I have gone months of working 80+ a week to get parts of my project done. When writing a paper I work less since it is a slower process. I have other classmates who just want a job when they graduate and they work 40h a week. In the end (maybe a 1-1.5 years from now) we may graduate at the same time but I hope to have 2-3 solid publications to their 1 mediocre one.

Some synthetic chemists work 80 or so in grad school, however there is a lot of down time waiting for this or that reaction to proceed. There are also a lot of lazy f***s who do nothing for 5 years and then somehow are awarded degrees.

I got my PhD in analytical chemistry and worked 40-50 hours a week. I'd like to think that I worked quite efficiently and made the most of my time. Most PIs won't care about your hours as long as you're productive.