I moonlight as an ER nurse as I finish my Software engineering degree next summer. I've worked in ER/Critical care for 15 years, and I've worked at over 25 hospitals as a contract nurse, and while your idea sounds good on paper, it's a medical/legal nightmare.
How fast you see a doctor in to an ER is not about being on a wait list. It's about how sick you are. If you're close to dying you get in right away. If you're not, we see you as soon as possible. Even then, it's not first-come first serve. And, if you're not here, you're not on the list, and there are no reservations.
And, I can't tell you how many people think they don't have something life-threatening and end up dead. And, there are many people who think that their illness is life threatening and it's not.
All it takes is for you to place one person on a wait list who ends up dead, and you're having a number of long talks with a law-firm. I'm not trying to be a hater, or flame you. I'm the last one to discourage an entrepreneur, but I'm really concerned someone will end up dead, and you'll have a big mess on your hands.
Please, rethink your business idea.