I think it can also take a while for your body to adjust. I once had some doctor-type tell me that if you have spent a long time sleeping on an irregular schedule, it can take up to six months for your day-night hormonal cycle to re-stabilize and your body to "expect" to be awake at a particular time. And I know that after college (three years of running on 6-ish hours of sleep a night) it took me nearly a year to get back to the point where I could bounce out of bed and be instantly awake and ready to go.
But I think it's totally worth it. I grew up with prescribed (early!) bed-times well into my teens, and I always feel like people under-estimate the health and productivity benefits of being really well-rested. Heck, most of them don't even know what it's like.
And sleeping from 9pm to 5am can buy you a pretty good window of uninterrupted work too... Love that feeling of having put in half a work day when everyone else is just rolling out of bed...
OK, I know I'm weird.