While it’s felt like we’ve been eagerly anticipating the outcome of the midterms for weeks, a good thing to keep in mind on election night is that there’s a lot that we may not know immediately because of how much time it takes to process ballots.

That delay won’t be a sign that anything has gone amiss, but the result of needing time to count votes, including mail-in ballots, which often take longer to tally because many states can’t start processing them until Election Day. Since each state also establishes its own vote-counting policies, and has different polling times, some states are also poised to be faster than others when it comes to reporting their returns.

Due to all this variability — not to mention a range of different time zones — the results will be staggered, and each party’s respective leads could shift significantly in the process. Here’s a rundown of a few things to expect as we wait for election results on Tuesday evening, and later this week.

Several states — including key swing states — may not be called on election night

Because of the time it will take states to process mail-in ballots, it’s possible several states won’t be called on election night, especially if the races are close. Wisconsin, for example, can only begin counting mail-in ballots on Election Day, so results won’t become more clear until that process is underway.

While it’s not an exact parallel, the 2020 election could offer a preview of when we’ll see returns from different places. As the New York Times explained, the presidential election results in 16 states still hadn’t been called as of midnight eastern time on Election Day that year. Notably, key swing states — including Pennsylvania and Nevada — didn’t have their races called until the following weekend because both places were still counting mail-in ballots, and both presidential outcomes were within less than 5 percentage points.

Depending on how tight the contests are this year, we could see similar timing, or a faster call if it’s clear that particular elections are a landslide. Additionally, fewer people may use mail-in ballots this year because there are fewer concerns about voting in-person due to the pandemic, another factor that could contribute to faster results this cycle than last.

Beyond counting of mail-in ballots, the timing of poll closures in different states could also affect when results come in. The first polls to close will be in Indiana and Kentucky, where some polls will shut down at 6 pm eastern. The latest West Coast polls will stay open until 8 pm local time and 11 pm Eastern, so many of those states, along with Alaska and Hawaii, won’t even begin reporting returns until later into the evening.

In general, states like Florida and Colorado are typically expected to report results faster because they’re able to begin counting mail-in ballots before Election Day, while states like Washington take longer because they can’t begin counting mail-in ballots until the polls close, and because they give voters more time to submit them. Below is a preview of when to expect results from some of the biggest swing states:

Pennsylvania: Polls close in Pennsylvania at 8 pm Eastern and results could take longer because the state does not begin counting mail-in ballots until Election Day. In 2020, Pennsylvania’s presidential election results were not called until the Saturday after the election, a dynamic that could be the case again for races that are particularly close, as the Senate race is expected to be.

Arizona: Polls close in Arizona at 7 pm local time / 9 pm Eastern and results could take longer because a high proportion of the state votes early and has until election day to drop off mail-in ballots. The state is able to begin counting mail-in ballots as they are received, but could take more time to process last-minute ones. In 2020, Arizona’s presidential election results were not called until nine days after Election Day, and the state could need more time again this year if many voters submit their ballots on the later side.

Georgia: Polls close in Georgia at 7 pm Eastern, and results could come in more quickly from the state this year because of rules changes that enable it to begin processing absentee ballots earlier than it did before. The closeness of the Georgia Senate election, however, could mean the outcome may still take longer to become clear. In 2020, Georgia’s presidential results were initially called by networks 10 days after the election, and reaffirmed six days later after a recount. It’s also possible candidates in the Senate race could go to another run-off on December 6 if neither wins more than 50 percent of the vote.

Wisconsin: Polls close in Wisconsin at 8 pm local time / 9 pm Eastern and results could take longer because the state isn’t able to count mail-in ballots until Election Day. In 2020, Wisconsin’s presidential results were called the next day, which could happen again this year depending on how tight the Senate election is.

Nevada: Polls close in Nevada at 7 pm local time / 10 pm Eastern and results could take longer because voters can postmark their ballots as late as Election Day, delaying the count. In 2020, Nevada’s presidential results were called the Saturday after the election, which could be the case again for the state’s heavily contested Senate race.

It might initially look like one party’s candidate is winning a race — but that could change

As results come in over the course of the next few days, the leads that each party’s candidates have could also shift: In some states, for instance, Republicans may initially appear to be winning because in-person voting is counted earlier and skews GOP, but Democrats could overtake them after mail-in ballots, which skew Democratic, are factored in.

That’s a dynamic that experts have warned about in states including Pennsylvania and Wisconsin, each of which has a tight Senate race. Neither state can count mail-in ballots until the day of the election, so those outcomes are likely to come in later than the initial in-person votes.

That set-up could create what’s known as a “red mirage,” suggesting that Republicans are initially winning, an outcome that could potentially change after more mail-in ballots are factored in. Earlier this year, former Fox News editor Chris Stirewalt testified in front of the January 6 Committee about this phenomenon, and how it was amplified in the 2020 election because more people used mail-in ballots that year. In 2020, Trump sought to exploit this dynamic by prematurely declaring victory because of early leads he had before the votes had fully been counted in battleground states.

As New York Magazine’s Ed Kilgore writes, it’s important to be on guard for candidates trying to use the same strategy to again falsely declare victory before all the ballots have been counted, especially in swing states like Pennsylvania, Wisconsin, and Michigan.

We might not know final Senate and House breakdowns

Beyond the specific timing issues that could result because of each state’s unique ballot-counting rules, there are other factors that could delay when we know the final breakdowns about House and Senate control.

If the Georgia Senate race goes to another run-off this year, it’s possible we won’t know which party has the Senate majority until after that race takes place on December 6. In Georgia, the Senate race automatically goes to a run-off between the top two candidates if no candidate wins a majority of the vote in the general election.

Additionally, it could take longer to finalize other outcomes if races are particularly close and a recount is triggered. In over 20 states — including Florida and Ohio — a recount automatically takes place if candidates are within extremely narrow margins of one another, usually at least 0.5 percent or less. Candidates are also able to separately request recounts if the results are close enough in other states.

Republican National Committee Chair Ronna Romney McDaniel signaled over the weekend that Republicans intended to utilize different avenues, including recounts, to verify and challenge election results that are not in their favor as well.

“Listen, you should have a recount. You should have a canvas. And it’ll go to the courts, and then everybody should accept the results. That’s what it should be,” McDaniel said in a CNN interview.

Attempts at legally challenging the results, or disputing mail-in ballots — a strategy that Republicans have already begun to employ in Pennsylvania, Michigan, and Wisconsin — could lead to major delays in officially settling races, meaning it could be weeks, or longer, before the final results are set as well.