I skimmed through ABC coverage of the 2018 midterms, and man, it was more chaotic than I remembered. Mail ballots seemed to come in late. This was especially true in the western states. Also Connecticut governor race appeared to lean republican at 1:30 am, because they were so slow on the count.
The ABC team seemed to have written Tester off on election night in Montana, and were hyping the hell out of Trump and Rosedale, just because of republicans doing well in red states in the senate earlier in the night. Same goes for Sinema and Rosen to a degree in Arizona and Nevada. All 3 ended up winning, but it wasn't called for them on election night coverage, so they got some negative spin.
Again by 1:30am, Democrats only had +26 in the House, and Nate Silver projected that they would only get around 30 total. When all the vote was counted, they ended up at 40+. So yeah, it could be a long night if some of the faster counting states are close and nobody wants to make a call.