I'm like you - I need 7-8 hours of sleep a night and I'm not a night person. I drive DH nuts because if I'm up until 11PM, I'm about ready to drop! We have a lot of night owl friends. I'm also up at 4:30 to workout before work as it's the only time I'll get a chance. I'm in bed my 9PM most nights, and asleep on the sofa by 8:30. Party animal - eh? :P

I've also trained for a half and know how physically demanding it is. Really listen to your body. If you need a break (on those days where you're so physically and mentally tired that you think you'll shatter if you move), take one. It won't hurt you to miss a short run or to miss a bike ride once in a while. And tossing in a "recovery week" every three weeks or so where you don't do a run over 6 miles and you generally take it easier is a great way to keep up the enthusiasm and momentum. I have a friend training for a marathon who does her long run every other week and it seems to really help her.

Good luck to you! I hope everything goes well!!!!