One thing I found with DD1, was that by changing her bedtimes she actually slept longer. If she went to bed at 7, she would wake up about 6 and because it was daylight she would want to get up. But if I put her to bed EARLIER, about 6 - 6.30 she would wake at 5 - 5.30 when it was still dark and go back to sleep!

Might be worth a try.