90 hours/week = 18 hours/day (assuming 5-day work week). That leaves only 6 hours for other chores, travel and sleep. This is not sustainable.
So I'll assume people who can pull off a 90-hour work week work all 7 days of the week which would amount to 13 hours/day. That still leaves sufficient time for a 7-hour sleep and 4 hours of chores and entertainment.
Now, if you are your own boss where you decide the scope and the deadlines, the work is going to be fun and I can understand that you would not mind working 13 hours/day. But I don't think working 13 hours/day for a boss or a company that considers me a cost in a business transaction of buying my skills is going to be fun.
So I'll assume people who can pull off a 90-hour work week work all 7 days of the week which would amount to 13 hours/day. That still leaves sufficient time for a 7-hour sleep and 4 hours of chores and entertainment.
Now, if you are your own boss where you decide the scope and the deadlines, the work is going to be fun and I can understand that you would not mind working 13 hours/day. But I don't think working 13 hours/day for a boss or a company that considers me a cost in a business transaction of buying my skills is going to be fun.