It depends on a few things. Yourself (main factor), your PI, and type of research.
You can usually work as hard or as little as you want. The drawback of not working hard is that you might have spent two years with little output and that may be a red flag. Most people who do research have very flexible schedules but still end up working pretty hard because deep down they are goal driven people.
The other factor is your PI. Sometimes PIs can be hardasses, sometimes they will leave you alone to work at your own pace. Obviously if you have a micromanager who expects email replies within the hour, your life will be less free.
The type of research also factors into your lifestyle. Some don't do research at all and instead do public health school, business school, etc. You can do some research that is relatively comfy, such as clinical research, outcomes, etc. Some basic science projects will have you in the lab to take care of cell cultures or animal maintenance. Some projects with human patients can be bad... if you need to collect blood samples for appendicitis patients or something you might be on call 24/7 and need to come in during the middle of the night to consent someone for research.
So it varies a lot. I guess you can look at the past residents and see what type of things they published to get an idea of what they expect from you. If they are publishing in Nature and Science on a regular basis, you can expect your research time to be pretty busy. On the other hand if they are publishing case studies in throwaway journals you know you're gonna be chillin.
In my case I work fairly hard and have been fairly productive. My life is still about a million times better than during clinical years. I work about 50-60 hours a week, a lot of that just surfing the web. I have been able to get time off work almost anytime I want, as long as I plan somewhat in advance and schedule my research stuff around it. It has been a nice break for me, and I am really a lot less toxic than I was before entering the lab. I am however a bit jealous of my former co-interns who are now chiefs and applying for fellowship.