My DD dropped to one nap at about 15 months - from memory it took maybe a month for her to get used to the new routine and settle into it. After that it was fine, she never needed an extra nap unless she was poorly.
She is now nearly 3 and dropping this final nap seems to be the most long, drawn out process. In about April (when she was 2 1/2) I noticed it was taking her longer and longer to fall asleep at night, and she was waking up earlier and earlier. When her wake ups got to 5.15 I decided to try her without a nap, apart from the odd snooze in the car. And for the first 6 weeks it was great - sorted out her night time sleep and she seemed fine in the day. After this she sometimes started getting a bit stroppy and hard work so I reintroduced an occasional nap - not every day, but just when she seemed tired. So she was having probably two naps a week on average. Over time this seemed to be phasing out, and I thought we were finally properly loosing the nap.
But about three weeks ago she became really hard work again, much grumpier than usual and started having loads of accidents, despite having been potty trained a while. I realised she was shattered, and so reintroduced the naps. We are now back to her napping 4 times per week (the other 3 days she is at nursery and she will not nap there!) and also sleeping 12-13 hours a night. Now she's been doing that a couple of weeks she seems much happier and back to herself. But it just seems odd that 4 months ago she seem to be fine on less than 12 hours sleep over a day, and now she is needing 13-14 hours again.
I just wandered if other people had found the same thing? I guess it isn't a big problem, I don't really mind if she naps or not. But I feel like I am constantly getting it wrong and either wrecking her nighttime sleep, or letting her get absolutely shattered.