Just an idea, but maybe you could take DS to bed with you at 9pm. Have him lay in your bed, with the lights off and nice and quiet. If you do this over a few days, he may start to realise that 9pm (or whichever time you chose), is quiet time and time for sleep.

I personally have let Lach decide his own sleep routine. He has decided to go to sleep between 8 and 9, wakes up around 3am, and then 6am, and sleeps until 9am. He likes letting mummy have a sleep in
I am not too worried about him waking a few times a night. He's only 6 months old, and I know that I get thirsty during the night and need a drink. I just figure that he won't truly 'sleep though' the night until he is around 5 or 6 years of age, when he realises that sleep is good. lol
I am so fine with Lach waking twice a night, rather than every hour and a half like he did for the first 2 months. LOL I find I am always trying to think back to those days
Good luck
I would be very very happy with Lach going to sleep at 11pm and sleeping through till 9 without waking.

xxoo