Hey,
I also have a 9 months old, he is sleeping through the night but waking at 5am. So this will not be an expert advice.
I would try increasing his activity time for 15 minutes and see what happens. I think that if you get a bit longer naps during the day it will help with night as well.
I had to teach my boys to fall asleep independently to get them to sleep TTN but that may not be the case for you.