15-18 Months
The biggest question, how do you know its time to switch to one nap?
Now, as you may recall I started doing my own version of a 5 hour schedule, where he started going down for his first nap at 10:00 and his second nap at 3:00. At around 15 months there was about a week time frame that he was very fussy about napping during one or the other nap. I decided to move his nap times up an hour and it made a WORLD of a difference. So for three more months he slept at 9:00 and 2:00 keeping all the feeding times the same.
When 18 months rolled around, (and the fact that I was due with our second child had some what of a factor in this), we went through another week of inconsistent napping. He wouldn't sleep for one or the other nap. I decided it was time to move to one nap between 12:30-1:00. I also transitioned him to a toddler bed. My theory behind putting him to a toddler bed was that he would be tired enough by only taking one nap that he would stay in his bed and OH did he stay in his bed. We had one incident that he locked himself in his room once, and we had to bust the door knob, but after that, it was really smooth sailing!
I think you will notice, that a Babywise kid is a lot more obedient. My oldest was very good when I would say, "It's time to take a nap, lay your head down, go to sleep and stay in your bed." He would stay in his bed. On those rare occasions that he would come to the door, all I would have to do is tuck him back in and say it again. If it happened again that same night, it really just took a firm Daddy's voice of "Go to bed" that would keep him in his room (haha). But really, it would usually only happen once, if it happened at all, and he would stay in his bed.
Consistency is so great for children! Be consistent. If you noticed in my earlier writing, it would be a week before I tried something different with his sleeping routine. Kids will go through phases and thats OK! Be patient and wait it out. If it's longer than a week, try something different. I remember at one point I put a blanket over the window in my sons room, so it was darker for him to sleep. Yeah, I had to wean him off it, but at least he got back to normal sleeping and weaning him wasn't too difficult because he knew it was still time to sleep.