I'll give you the BCG perspective - It definitely requires conscious efforts to protect time for relationships, but most people do it well. I'd say it's hard for new consultants to work in consulting, maintain time for relationships and get involved in activities/hobbies. It gets easier over time, but you definitely need to prioritize the non-work things which are important to you.
During the week - here is where you really need to prioritize your time for phone calls, and you really can't consistently plan on being free at any given time. Thursday nights tend to be well-protected on most case teams, and people really try to get home by a reasonable hour on Friday (typically by 5pm, in my experience). I know some people who have managed to work local most of their careers, but you can imagine that it means not always landing your "dream case". And even if you are local, you never know what your hours will be like.
During the weekends - these are quite well protected, and one amazing perk is alternate travel (rules are getting a bit stricter on this being a taxable benefit, but still better than paying totally out of pocket). Sunday nights I found myself preparing for the week a bit, but I don't think that is unique to consulting. From Friday evening - Sunday evening, I generally didn't need to do anything related to work. Maybe 10-20% of the time, I had some work to do, but it wasn't much.