I don't know about it being normal but it's not out of line. I tend to work 10 hours/day 5 days a week and have been doing so for the past 35 years. There have been times when I've worked 60-70 hours/week and I can tell you that's less productive than working 50 hours/week because fatigue makes things worse - those extra hours are actually working against you. As a result I've learned you can't work more then 10 hours/day and you need at least one day off per week. That means the max you can work is 60 hours/week, and that's not sustainable. You can do that a few weeks but you can't sustain that. 50 hours/week is both sustainable and doesn't work against you. As with anything, YMMV. 50 hours/week is what I have found I can sustain. Your sustainability rate may be more or less. You need to find what works best for you.