How do we end the culture of “endless hours at work”? In many of the research groups I’ve worked at or visited, there is a culture that endless hours in the lab equal successful researcher. (I am in a theoretical field, so requirement of long-running experiments are outside of the picture. Let's ignore them in this discussion.) In chemistry, a widely-known example of this culture is the following letter:
               

I would like to provide for you in written form what is expected from you as a member of the research group. In addition to the usual work-day schedule, I expect all of the members of the group to work evenings and weekends. You will find that this is the norm here at Caltech. On occasion, I understand that personal matters will make demands on your time which will require you to be away from your responsibilities to the laboratory. However, it is not acceptable to me when it becomes a habit.
I have noticed that you have failed to come in to lab on several weekends, and more recently have failed to show up in the evenings. Moreover, in addition to such time off, you recently requested some vacation. I have no problem with vacation time that is well earned, but I do have a problem with continuous vacation and time off that interferes with the project. I find this very annoying and disruptive to your science.
I expect you to correct your work-ethic immediately.
I receive at least one post-doctoral application each day from the US and around the world. If you are unable to meet the expected work-schedule, I am sure that I can find someone else as an appropriate replacement for this important project.


I have fallen prey to this during my PhD, doing very long hours. Now that I manage a research team, what is good advice to help fight this culture in my team? (Obviously, I don't want students and post-docs to get the message that little work is required either.)
Things I already do to that end:

When a new group member comes in and they get the out-of-hours building pass (for Sundays and late nights), mention that they are not expected to use it on a regular basis.
Avoid planning meetings at unusual hours (bank holidays, week-ends, etc.)
In the different groups I worked in, their respective cultures were always the result of the behaviour of the leader. So lead by example. In particular, some useful hints from my experience would be:

E-Mails: don't send e-mails in non-office hours, especially not requests for help with something. No e-mails on weekends and late night are a signal which everybody "gets" after a short while. 

Social activities: support group's social life. A group hike to nearby mountains (in office hours on a working day!), or a joint trip to a museum sends a signal that taking time off is an important part of one's life. We used to do it on occasion of having a guest researcher (for a study stay, or just a seminar talk). It's good for group's cohesion and again tells people that rest time is also very useful. 

Personal relationship: care for private lives of your group members. Build relationship with their families. Speak to them about their personal activities, about their vacations, kids, etc. and do not forget to give back and speak about yours. These kinds of discussions send a powerful signal that you perceive time off in a positive way and even encourage it, since you take it as well.

Plan well ahead: clear plans and roadmaps in projects allow people to plan their time off as well. Nothing more annoying than a spurt interfering with one's private life to deliver some report, because the boss didn't care to tell the group ahead.

Time in the office: being in computer science, where I do not need to spend time in a lab and can easily work anywhere, I was always lucky to have bosses who cared for deliverables, rather than for my time in the office. After all, most of my good ideas are born in weird places, such as under shower, while on a bike, walking in woods, and by reading stuff outdoors. Making it clear with the group members that you care first and foremost for deliverables and are flexible regarding the actual time in the office (within reasonable bounds and respecting the local laws and regulations) works well. My experience is also that people tend to deliver better if they are given the power to plan their time and process, rather being forced to mantinels set by their supervisor.

Generally, I found it always very comfortable in groups where having kids was something nice and for what the group leader and members cared. Nothing is worse than a group where work interacts negatively with one's family life and where going home before 6pm to care for kids at home is perceived as something bad.