Oh man, Cornish hens are different from full size chickens (note that they are chickens still). The skin in thinner and there is less fat, the skin will render nicely at many temperatures. Personally, I prefer to grill them, split and marinaded, then grilled over a high heat. That being said, I have done them whole as well.
I wedge some garlic cloves and a large lemon wedge into the body cavity then rub with a little salad dressing and toss into the cooker at 325F. I have never timed them, I use a remote thermo and take them out when they reach 155F to 160F. They don't hold so well. I tend to adjust dinner for when the birds get done. I would give them 45 to 50 minutes as an estimate
me: I don't drink anymore
Yelonutz: me either, but, then again, I don't drink any less