I don't feel like I "have to" work 6 days a week - I do it because I want to. You may say that this is just because I'm a cofounder, but that's not true - I did the same thing at past startups where I was an early hire, but not a cofounder. Because I enjoyed the work, found it meaningful and loved learning. This is the kind of person we're looking for.
Maybe you don't need highly experienced senior people at the stage you're at now, but you will at some point, and by setting this expectation now you're setting yourself up for failure in the future, IMHO (which is why I'd be questioning you heavily if I were an investor).