my dd2 started her 2 - 1 switch (or needing the switch...i didn't clue in until 11.5 mos that that was what was causing all her issues) at 10 mos. ugh! 6:30 would be heaven for us too, as well as an 11.5 hr night. the most she's ever done (without a long NW) is 11 hrs and the latest she's slept since 9 months is 6:10 am and both those were single occasions! for a while we had 4:00 EWs. Oh my.
anyway, cutting the AM nap is more for the EWs, not to extend the PM nap. she'll almost always take a good PM nap (sometimes over 2 hrs), especially if AM is short. if not for the school runs etc. i think i would just go cold turkey on the 1 nap like i did with dd1. with dd1 if she ever fell asleep in the car, even for 5 min, she would refuse her nap all together. but, she was a great night sleeper, terrible napper so who knows how dd2 would handle that...