Nah, that's what proper community beta testers do. Otherwise you just don't sign up for it. If you've got work to do, you cant beta test in this time. It's that simple. There are enough students or people working in shift system that can easily make up this time.
I totally disagree. I've betatested games in my spare time with far less hours, that went weeks. As I said, if you get paid for it, 8 hours is ok. Otherwise you compensate by the amount of people from your community.
I assume that you have that much spare time on your hands, otherwise you wouldn't assume that many people have 8 hours or more free to do anything. Most peoples lifes are cut in 8 hours work, 8 hours sleep and the rest is spare time, going into eating, possibly family, etc.
I however agree that people should bring time, as much as they can spare for the game and also report on what they find and not just take it as an opportunity to play it for free.