Sleep is individual to every person, asking how many hours of sleep I get is really irrelevant to YOUR personal needs.
There is great research showing a very small subset of the population only need about 3 hours a night to function OPTIMALLY. How great would that be?
In general, a person needs about 8 hours to function optimally, but many can get away from 6 hours. You will have to experiment for yourself and see if waking up 30 minutes earlier than normal effects you in any profound way.
Keep a log on a scale of 0-5 of how restful you thought your sleep was. If you wake up extremely groggy, cant function throughout the day, and feel like hell by 2pm give yourself a 0. If you have energy to spare throughout the day give yourself a 5. Take note of these numbers, how many hours of sleep you got, and also be aware of other factors that may influence it (getting up in the middle of the nights, stress, etc...) This isnt exactly "scientific" but you cannot adjust what you do not measure.
In a few weeks time you should begin to find patterns that lead to optimal sleep and performance throughout the day for your unique situation.