This can vary highly by firm, but I guess it would ultimately depend on your assignments and the expectations of the firm as well as of your own standards.
The firm I was at was a small one with five attorneys at most who gave me work to do. This could range from boring to stressful, but every day I was expected to clock out at 5pm. We also closed on weekends, and we never had any emergencies to warrant coming in those days anyway. I will say sometimes I would leave at the end of the day worrying about what I had on my plate the next day, but it never truly consumed me. I still had time to be on a competitive dance team and hold the position full-time. In the end, even through all the stress, my balance was really nice.
It was fair. I say fair because there was times I would be the first one to come in and the last one to leave during the week. At busy times like this, I would also be asked to come in on the weekends to work on special cases quickly approaching a deadline. Being asked to work late would make it difficult to give focus on my schoolwork. It felt as if my schedule was always being adjusted to get things done at home.