DS is almost 12 months and still doing two naps (around 9:30-11 and 2:30-4--very rough estimates--totally depends on when he wakes). He used to be up from his pm nap by 3, but its gotten later--some days he doesn't even go to sleep until 3:30 or 4, but I still let him take that last nap because he's always so tired and bedtime would have to be REALLY early if he didn't.
My personal opinion is to not push the 2-1 nap change, but wait until they are actually refusing the second nap regularly. Just because I know that they will go back and forth for awhile and I'd rather not fight it early and then have them overtired off and on for months. They need more sleep when they hit growth spurts, are going through developmental stuff, etc. . . And there is a lot of that going on around one year.
And a lot of the time, even if DS takes a late nap, he is still tired by 7 or 7:30 for bed anyway--He still needs the sleep, just takes it a little closer to bedtime, so it still works to do two naps. I've been surprised since he normally goes 3-4 hours until bedtime.
HTH!
~Kim