Hi A.,
It seems to me that 9 hours isn't enough for a baby that age. My son's father used to go in at 5 AM when my son woke up because he didn't see him all day and wanted to spend time with him. Consequently, my son at age 8 still has difficulty with getting enough sleep since when he wakes up before 6 AM he can't get back to sleep. He wakes up and lies there feeling "exhausted" and then he feels "tired at school." The moral of the story: make sure that he isn't hungry and let him learn to get himself back to sleep even if he has to cry for a few days. Maybe you need to go in at 11 PM and give him a feed before you go to bed so that he won't be hungry at 4:30 AM. Just don't wake him or talk to him--nurse and back to sleep.
I never found that when my son went to sleep later that he slept later in the morning. I think that everyone has a natural rhythm and some of us are early risers, so going to sleep later just guarentees crankiness. Put him to bed by 7:30 for a couple weeks and don't go in until 6 AM if he wakes up at 4:30--he may surprise you and end up getting 10 1/2 hours.
Maybe you need to go to sleep earlier, too, so that you get more sleep during the "adjustment period." Again, the key is to make sure he isn't hungry at 4:30 and let him figure out how to go back on his own.
A.