As far as I know, most people in publishing generally have 'normal' working hours. Yes, they work outside of these hours when necessary - staying in the office late to call someone, or arranging a meeting out of work hours, but I don't think it's a matter of course to keep people in the office over the weekend. They're more likely to take a pile of work home than be in the office on a Saturday.
This is just my experience from being a lowly editorial assistant some time ago at a publisher in the UK. I sometimes went to work early to call Australian authors, or stayed a bit late to talk to US authors, and occasionally I went to events arranged in the evenings. It was common for my colleagues to stay late in the office if deadlines were imminent. However, in two years I only heard of one person go in on the weekend - just once, and they were more dedicated to the job than anyone else I knew. I regularly took manuscripts home, but would never have gone into the office at the weekend. Then again, I was just an editorial assistant. If you're a more senior editor with big authors, I can see why it might be necessary on occasion.
Generally though, don't wait by your phone on a Saturday night, expecting it to ring. Unless it's super-urgent, the editor will most likely wait till Monday to offer a contract.