If you spend 80 hours you're being inefficient.
If you spend 20 hours (and they're being charged for value,) they feel they were deceived.
Selling your hours to anyone truly seems like a lose-lose situation.
I meant more like 80 hours a week. It is, in my experience, difficult and cumbersome to charge for more than 40 hours a week since it kinda disrupts the usual cadence. You can do it sometimes for deadlines but wouldn't want to make a regular habit of it