The election is run state by state.
The rule (that Networks follow) is that no results of any kind will be released for a state until the polls close for that state. That means the for the states that close the polls at 7:30 (which include the all important North Carolina) you will see results shortly after.
There are two types of results you will see tonight.
There are exit polls. These are not official, but are generally pretty accurate since they ask people leaving the polls (i.e. real voters) who they just voted for. The exit polls are conducted throughout the day and are released by the network as polls close.
Then there are the official results that are tabulated by the machines. These generally take an hour or two to start trickling in. These are released as they are counted.
So yes. Starting at 7:30 you will hear exit polls for some very important states that will give you a good picture of who is doing well and whose constituents are coming out to vote (i.e. if lots of Latinos are voting, you can assume a very good result for Clinton). Shortly after you will hear the official results.
So yes, if the election is very lopsided, they may even announce a winner before everyone has voted.