Most of my little ones start to transition around 13mth, to one nap. During the transition time sometimes the little ones are "11o'clockish" meaning that they need to eat early (around 11) then go to bed shortly after. At the moment I have one 18mth old in my care who still needs a morning nap (especially during growth spurts) but I also have a 15mth old who has never had 2 naps at my house.
My "2 nap kids" start to transition with a short (no more than an hour) morning nap 8:30 - 9:30... remembering that most of theses kids are up around 6:30 or earlier.
Then they go down for nap with the older children around 12:30.