Most of us have to be up at a specific time every weekday. Over the winter, it's usually 5:30 daily for me.
Instead of having a "bedtime" just focus on your "wake-up time" and for crying out loud, go to sleep when you feel yourself getting tired. This eliminates those tossing/turning/book-reading/TV-watching moments in bed. It also eliminates those nights where your ass is dragging all night long and you finally see your bedtime on the clock and slog to the bedroom. Those are the nights that lead to abuse of the snooze button, or worse!
At first, you might find yourself waking up ahead of schedule. If you feel up to it, try to go back to sleep until your alarm goes off. Likewise, you may still feel the urge to hit the snooze button at first. After a few days of this, you'll start to get in the groove.
I occasionally stretch my tired state out, but usually I reward myself on the other end by rolling the alarm forward by a half hour or so, if I can get away with it. I haven't hit snooze in years, and most mornings, I wake up right before my alarm goes off. I get 5-6 hours of sleep per night.
The temptation might be there to hammer out those last few lines of code, finish post-processing the weekend's photos, push yet another blog post out, or finish up your trigonometry homework. If those are things you really, really must do, you're doing it wrong.
Watch less TV (or Video podcasts, youtube, etc), unsubscribe from some of your RSS feeds, or find ways to combine your leisure activities. You can easily catch up on podcasts or IPTV shows while working out, for example. It beats being stuck watching old Marathon or Tour De France footage.
Sleep is variable, and it's definitely a big time-consumer. Polyphasic sleep definitely isn't for everyone, and it's not wise to cut back on your slumber to make room for fun-time. It destroys your productivity and can leave you dangerously unfocused while performing critical tasks (such as driving or executing commands as root on production servers).