At a very high level, an approximate average of all the partners I met in almost 5 years at McKinsey, worked from 9 to 9 (12 p.m.) every day, with a potentially shorter day on Friday. However, there is significant variability here. However, it depended on the project, because if I had a short 2-week due diligence project, I didn't have a weekend. It's really interesting to work on those projects because you're spending two weeks on whatever you're doing, but it's not a pace you want to maintain for too long.
However, in general terms, it was normally a 60-70 hour work week. My 2-year average was around 60 hours a week and I was only working one weekend due to a terrible DD illness. It really depends on the office and the project. San Francisco and New York work longer hours than I do in Chicago, but I did an internship at BCG the summer before senior year and found that they were working worse hours than most people I know at McK.
I've found friends in Bain who work harder on Fridays, but I work more during the week and relax more on Fridays or travel more.