British Prime Minister Theresa May last week set the precise moment that the U.K. would leave the European Union — March 29, 2019 at 11:00 p.m. — the two-year cutoff date after March of this year, when the British government officially conveyed its Brexit decision to the EU. But as the U.K. becomes increasingly mired in the difficult issues surrounding its exit from the European economic and monetary union, to many, May’s 16-month timeline is starting to look overly optimistic. (Indeed, May faced pressure from her own party to scrap the exit date shortly after proposing it.) Three critical questions remain to be resolved before the next stage of the negotiations, according to Brendan O’Leary , professor of political science at the University of Pennsylvania. One has to do with protecting the rights of British citizens living in the E.U. and E.U. citizens who reside in the U.K.…