I have found with my LO that if he goes to bed later than 6.45 then he wakes up MORE during the night. It has taken me ages to figure this out.
I used to put him to bed 3 hrs after he woke up from his afternoon nap but since returning to work (i finish at 6) I have discovered that the sooner I get him into bed the better. I aim for about 6.35 - 6.40 and he goes to sleep straight away, any later and it's a nightmare trying to get him to sleep. He normally sleeps till about 2am, then through to about 7.30 and he still has 2 x 1.5 - 2 hr day sleeps.
HTH