A reminder about the timing of the exit polls: The Edison Research exit poll, which is what most of the networks use, is being conducted right now, and at 5pm Eastern (just under 2 hours from now), Edison will be sharing their preliminary results with the networks. So then, starting at around 5:10 or 5:15pm or so, we'll start to see various news stories pop up along the lines of X% of the electorate is whites with a college degree, or Y% approve of Trump's performance as president, or whatever. But they will not release the full toplines of the exit poll for individual races until the polls start closing.
The wrinkle this year is that both Fox News and the AP have split off to do their own thing. They will not be using Edison, but are instead going with a new system called VoteCast, that's mostly based on online and phone polling. Details here:
https://www.vox.com/policy-and-politics/2018/11/6/18067982/exit-polls-results-start-2018-midterm-electionsI don't know when we'll start to get VoteCast numbers.