I thought I would let you know about my daughter. We transitioned to one nap at 12 months. She was starting to anyway and we were going to be having over half the week of not getting to nap in the morning until noon anyway. She did okay during the transition, but her naps were so short. 1 hour to 1.5 hours. This lasted from 12 months to 18 months. She is now napping for 2 hours pretty consistently and sometime will sleep 2.5-3 hours. So apparently some kids can make the transition to one LONGER nap sooner than others. With us it took 6 months.
And dd is usually awake by 6:00. Some days we get lucky and she sleeps longer. But here is my philosophy that is working for us. I don't get her out of bed until 7:00. She can doze for that hour (and if she is awake at 5:00-5:30 like some mornings, 2 hours), talk, read her board books that I leave in her crib. That is her time, but I do not go in to get her. The only exception is if she is sick, etc. It took a couple of months of pushing the time that I went in to get her up, but she doesn't complain at all until after 7 now. I don't know what I will do when she is potty trianing and needs to get up and go as soon as she gets up. (Take her to the potty and then tell her to play quietly in her room until 7?) I am usually up anyway. I set my alarm for 5:30 so I can get ready and do my devotion before she gets up. If I don't get those done before she gets up, it is difficult to get them done.