I didn't read all the other responses, but I will say that I thought we were the only ones dealing with this since none of the moms I shared my struggle with could help.
We went through the same thing and what worked for us in curbing the pattern was to start prepping for bedtime at 7:00pm instead of 6pm. At one point during the figure out process I just asked him... 'are you ready for bed?' - his answer was no, so I thought let's see where this goes - once won't hurt. I told him in front of daddy "OK you can let us know when you're ready" - all tv's were off and there would be no playing, all three of us just sat in the L/R and talked 1) he realized that we were boring and didn't do much of anything after he went to bed 2) he thought he would get to play if he stayed up and quickly learned that was not the case. He told us he was ready within 20 min and that is what finally led us to believe that his bedtime would change. Mind you, this question has been asked a couple of time and we follow through with the same actions.
As I mentioned above, we start the routine around 7pm (shower, teeth, potty), read from about 7:30-7:45. Turn off lights and talk about the days events til about 8:00 - 8:15. He's out by 8:15 - 8:30 every night and up anywhere between 6:30-7:30 every day. So far so good and this will only hold true until he goes through another change :)
Hope you find something that works for you!!