Polls close about 10 p.m. local time (5 p.m. Eastern) on Thursday, and no formal exit poll will be released. This means that only when the first vote counts start being released about midnight U.K. time, will we get our first picture of what the result might look like. Votes will be counted until one side reaches a number that is mathematically unbeatable, which may take a while, given how close the vote is expected to be. It's thought that from early morning U.K. time, perhaps about 2 a.m. for those of us on Eastern time, the final outcome of the vote should be clear.
This is a little complicated. No country has ever voted to leave the European Union before, and it's not exactly clear how things should proceed.