The polls close at different times in different states and it is only loosely related to time zones. Some states are split geographically in terms of when the polls close (ie: parts of the Florida panhandle keep voting one hour later than the rest of the state).The only rule in the US is that the networks will not put out exit poll data on a particular state while some polls are still open (ie: in 90% of Florida the polls will close at 7pm EST, but they won't project anything until the panhandle polls close at 8pm EST).
The US does NOT have any of the barbaric and silly laws we have in Canada that try to prevent people in California from knowing how the vote count is going on the east coast while polls are still open on the west coast.
At 7pm EST several states (mostly in the south, plus Indiana and Kentucky) will close all their polls and the exit poll projections and counts will quickly start to flood in.
I am having people over and I have a bottle of Dom Perignon that I have been waiting 10 years for an occasion to drink!