My son just turned 21 months and I think we are going through a transitional stage regarding wake up, nap time, and bed!
I'm sure part of that is due to our family being in "winter mode" (daddy is laid off for the season and we don't get up at 5am anymore!)
We had been very regular...up at 5am, breakfast at 6am, nap at 10am, lunch at 1pm...dinner was approx. 5:30pm and we started winding down for bedtime at 7pm. Lights are dimmed, in the jammies with milk and snack, etc...books were read at 7:30 and despite the fact I had to be a bit of a Super Nanny to keep putting him back into bed, there were no tears or real struggle, and he'd be asleep by 8pm.
We got really off schedule with the holidays and Daddy not working, and I'm nearly 8 months pregnant and just DON'T have the energy to chase the kid back into bed...so he was napping at 1pm, going to sleep at 10 or 11pm...it was a mess. We live in a railroad apartment, so we struggle with bedtime regardless, since none of us have privacy or solitude.
The moral of the story is, I think you're right, that at this age it's a bit of a transitional thing. I used to be able to get him to bed super early, and now it's more like 8pm-ish. I've started setting our alarm in the morning to help us get back on schedule, no matter how exhausted we are and it's definitely helping! Now I just wish I could get him to sleep through the NIGHT!!