I wonder if there's a difference between "establishment" and "adoption."
If so, when Virginia adopted ("chose" = ad + opt) the Constitution four days after it was "established" according to Article VII, George Washington was indeed a citizen at that time. The time of adoption in Virginia was June 25, 1788, according to http://www.yale.edu/lawweb/jbalkin/arti ... iously.pdf
, and thus, my literal reading shows Washington to have indeed been eligible to hold the office of president.
But I suppose it could be argued that the Framers were not distinguishing between "establishment" and "adoption," although they well could have been. They were not unaware of the time element that was a part of daily life (the travel time between Philadelphia and elsewhere). So I think it's entirely possible that they *did* distinguish between those two nouns.
On the subject of NBC and parentage, I had thought the "strict" view had been that both parents had to at least be naturalized citizens, not that both had to be NBC themselves.