A couple of points:
(1) Like virtually everything in life, sleep has a sweet spot -- more isn't always better. E.g. this large-scale epidemiological study (http://www.ncbi.nlm.nih.gov/pubmed/20621406) of 56,000 people found the lowest health risks in those sleeping 7-8 hours. Too little sleep is correlated with health risks, but so is too much. Of course, the location of that sweet spot varies from person to person, and if you're training seriously you should definitely expect to need more sleep than the average joe. But once you're getting enough sleep for your needs and your activity level, you don't need more.
(2) It's virtually impossible to judge sleep needs based on a single day, or even a single week. If you're used to going to bed at 11, then one day you fall asleep a few hours earlier but wake up early the next morning, that may just be that your body is only used to getting 7 or 8 hours a night. The single most important thing you can do is establish a regular sleep routine that you can stick to, and that leaves you enough time to get all the sleep you need.
For example, plan to spend 9.5 hours a night in bed every night, starting and finishing at the same time. For the first few weeks or months, you may have trouble falling asleep or staying asleep. That's okay -- just read until you're tired enough to fall asleep. After a few months, you'll be in a regular enough routine that you should have a sense of how long your body wants to stay asleep each night. For me, I find that 8.5 hours is as much as I can use -- and 8.5 hours every night is infinitely better than 6 hours some nights and 10 hours other nights.