mine slept ard 11pm to 11.30pm when he was 3.5mths.
4mths to 4.5mth, he starts to get sleepy by 10.30pm.
He just cldnt sleep early no matter how tired he was.
Now 5.5mths, he sleeps before 930pm through the night, and I didn't even trained him
I just let him be. A happy baby is a happy mummy. So long he sleeps n drinks well, all is good