If you sleep 8 hours and consume 90 minutes showering, relieving yourself, eating that leaves you with 101.5 hours per week.

If you had to you could probably spend all this time running your mouth but probably not intellectual work.

This assumes that you have no responsibilities of any kind and everything is done for you.

Agreed that 90+ or 120 are just insanely difficult to do on the regular. I think I could have 1 such week per month, maybe once per quarter. One thing that might be a bit different in your example is if all 90 hours were for the same product. It might have been tougher for you to pay some time context switching between the two. Whereas, Elon Musk is doing all his hours for the same task. (Well, actually he's a terrible example because he probably has 100 tasks he does for 1 hour each week, but you get my point for the general case.)