Phineas and Ferb had more than 104 days of summer vacation to try to do it all, but they have at least one big adventure left: Meeting Milo Murphy.

The Disney characters will finally cross paths in “The Phineas and Ferb Effect,” the upcoming, hourlong crossover special featuring “Milo Murphy’s Law” and “Phineas and Ferb.”

The episode, which will kick off the second season of “Milo Murphy’s Law,” is set to air on Jan. 5 on both the Disney Channel and Disney XD.

The premiere date was revealed in a new video featuring “Weird Al” Yankovic, who voices Milo Murphy, discussing his current projects with “Phineas and Ferb” villain (and new podcast host) Dr. Heinz Doofenshmirtz.

“The story arc of ‘Milo Murphy’s Law’ has been designed from the very beginning to lead us to a big crossover with all the ‘Phineas and Ferb’ characters,” the shows’ creators, Dan Povenmire and Jeff “Swampy” Marsh, said in a joint statement. “We’ve planted lots of clues and Easter eggs in the first season, and we can’t wait for the fans to see these two worlds collide.”

In the long-awaited crossover, Milo and his friends Melissa (Sabrina Carpenter) and Zack (MeKai Curtis) must work together with their newly discovered neighbors — Phineas (Vincent Martella), Ferb (David Errigo Jr.), Perry the Platypus (Dee Bradley Baker), Candace (Ashley Tisdale), Isabella (Alyson Stoner), Baljeet (Maulik Pancholy) and Buford (Bobby Gaylor) — to stop a pistachio invasion.

Fans can also expect appearances by time travel agents Vinnie Dakota and Balthazar Cavendish, voiced by Povenmire and Marsh, respectively. The pair will also reprise their “Phineas and Ferb” characters Dr. Doofenshmirtz (Povenmire) and Major Monogram (Marsh).

“Milo Murphy’s Law,” which debuted in 2016, follows Milo, the fictional descendant of the original Murphy’s Law namesake, who suffers from an extreme case of “if anything can go wrong, it will.”

Disney’s “Phineas and Ferb,” which chronicled the summertime adventures of stepsiblings Phineas Flynn and Ferb Fletcher, ran for four seasons from 2007 to 2015.

Dr. Doofenshmirtz, who made an appearance in the first season of “Milo Murphy’s Law,” will be playing a larger role in the show’s second season as Milo’s new housemate.

Additional Season 2 guests will include John Ross Bowie and Cedric Yarbrough (“Speechless”) voicing shape-shifting alien buddies Loab and Khone, and Hal Sparks (“Lab Rats”) as Chaffe, a conspiracy theorist. NASCAR racers Rusty Wallace, Joey Logano, Ty Dillon, Ricky Stenhouse Jr., Erik Jones and William Byron, as well as sports announcer Mike Joy, will also guest as themselves.

Subsequent new episodes of “Milo Murphy’s Law” will air Saturdays on the Disney Channel and Disney XD.