I phoned my dr's office and they really emphasized that 11 months was too early for one nap. They said to continue offering 2 naps...once you make the switch to one nap, there's no going back.
So the last couple of days I've sort of followed Michelle's advice. We are keeping the morning nap to 1.25-1.5 hrs tops. I found that if I can get that afternoon nap in before 3pm, then we're ok. If we go later than that, we always have troubles. For example, this morning, he woke at 6am, so nap #1 was 9:15-10:30am. That means I can get nap #2 in by 2pm which is ideal.
On those mornings, like yesterday, when he wakes at 7am, then it shifts a bit, but if I can keep the morning nap to 1.25-1.5, we're still in the ballpark.
I hope this continues!