I disagree with your premise (that 80 hours a week is appropriate for a start-up). As an experienced developer (25+ years now), I'd put money on my code being

I disagree with your premise (that 80 hours a week is appropriate for a start-up). As an experienced developer (25+ years now), I'd put money on my code being more capable of pivoting quickly to a new product road map than the code of a less experienced developer. I've had clients/employers be amazed by how fast I could change fundamental behaviors of software I've worked on, and not because I put in 80 hours, but because the design starts out flexible, and I can adapt the work to the new requirements with minimal effort. Sure if you're ask your dev to make changes on a Saturday, the 80-hour employee will be there, but if he/she is still working on that major pivot by Monday, and I can make the changes in a few hours, and my code is more stable, then I still win. ;)