Here in New York the polls are open from 6:00 AM to 9:00 PM on election day. Every state is different. BallotPedia has a list of the times polls open and close in all of the states, all times on the list are local. Even after you have voted, this will help to keep track of which states still have polls open while watching the election returns.
In the major battleground of Ohio polls will be open from 6:30 AM to 7:30 PM Eastern Time. People in line by 7:30 PM will be allowed to vote even if there is a line slowing things down.
Pennsylvania polls will be open from 7:00 AM to 8:00 PM Eastern Time, and in Wisconsin they will be open until 8:00 PM Central Time.
Click here for the full list.