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The last time the Ravens needed a head coach, owner Steve Bisciotti took nearly three weeks to find one.

With John Harbaugh fired Tuesday after 18 years, Bisciotti doesn’t need to post a “help wanted” sign outside the team facility in Owings Mills. The Ravens’ vacancy will be the most coveted in the NFL.

But that doesn’t mean the process will move quickly. Here’s a look at the NFL rules and guidelines that will shape their search in the days and weeks to come.

Virtual interviews

The Ravens can start interviewing candidates not employed by another organization as soon as they have an opening. But, for coaches employed by other teams, the process is more formal.

Coaches of teams that didn’t make the playoffs can be interviewed virtually three days after their final game, meaning Tuesday or Wednesday for the league’s 18 nonplayoff teams.

The process is different for assistants on playoff teams. For the two teams with a bye — the Seattle Seahawks and Denver Broncos — virtual interviews can be held this week. The Ravens could interview Seattle offensive coordinator Klint Kubiak and Denver defensive coordinator Vance Joseph, both potential head coaching candidates, starting Wednesday. Those virtual interviews can be conducted through this weekend and are limited to three hours in length.

For assistants coaching in the wild-card round this week, the Ravens can have a virtual interview of up to three hours beginning next Tuesday. Coaches on the Houston Texans and Pittsburgh Steelers’ staff must wait to interview until next Wednesday, because they play Monday night.

In-person interviews

The Ravens can begin in-person interviews with assistants who are under contract with other teams on Jan. 19, unless those teams are alive for the conference title games.

Those coaches must wait until Jan. 26, when either they were eliminated from the playoffs or have a bye week before the Super Bowl. Coaches on the Super Bowl teams are allowed to be interviewed through Feb. 1 but are forbidden from talking to other teams after that until Feb. 9, the day after the Super Bowl.

Coaches on the Super Bowl teams are not allowed to interview in person with other teams during the bye week if they hadn’t done an initial virtual interview earlier in January.

No coach can sign a contract or agree to sign a contract until their season is completed.

Rooney Rule

The Ravens must abide by the Rooney Rule, which was implemented in 2003 to boost minority hiring. Before hiring a new head coach, teams are required to conduct in-person interviews with at least two diverse — minority or female — candidates who don’t currently work for the team.

The rules are the same for all coordinator positions, and clubs must interview one diverse candidate for any quarterbacks coach job.

The Associated Press contributed to this report.