Mitch Korn was discussing the monumental importance of a tenth of a second.

The Islanders' new director of goaltending, stopwatch in hand, was on the ice early on Sunday, working with the four netminders on Day 3 of the team’s rookie camp. The drill had the goalies moving side to side before dropping to their pads while still sliding right to left and back again. But before his pupils started, Korn emphasized how an improvement of a tenth of a second can mean the difference between making a save or not.

The Islanders hired the Bronx-born Korn, 60, who has worked with coach Barry Trotz since 1998 through their stops in Nashville and Washington, on July 26, a day after adding Piero Greco from the Maple Leafs’ organization as goalie coach.

“Three days is a really short time but I have enjoyed the time here,” said Czech-born goalie Jakub Skarek, a third-round pick in June, who departed later on Sunday to rejoin his team in the Finnish Elite League. “I got a chance to meet Mitch Korn, one of the greatest goalie coaches in the world. When I grew up, Dominik Hasek was my idol and I know (Korn) helped him in Buffalo.

“I was trying to listen as much as I can and ask him everything to bring those things back to Finland,” Skarek added. “I think every detail is huge that he told me. It’s great for me.”

Emanuel Vella, 20, who has played four seasons of junior hockey in the Ontario Hockey League, Evan Buitenhuis, 25, who played four seasons for Hamilton College, and Mitch Gillam, 25, who played in the East Coast Hockey League last season after four years of college hockey at Cornell, are the other goalies attending the Islanders’ rookie camp.

Skarek said he will stay in touch with Korn, as well as Greco and goaltending development coach Chris Terreri via Skype and e-mail during the upcoming season and hopes to take the lessons learned at the Northwell Health Ice Center into his first season in the Finnish league.

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“It’s not the big things,” Skarek said. “It’s the little details that can make a big difference in games. I’m glad I could work with him and the other goalie coaches here. I never really had goalie coaches around me.”

“You’ve got to look at those micro seconds,” Vella added. “In the video clips, it’s 30 frames per second. So that’s three frames [for a tenth of a second]. That’s a lot of time in terms of the puck going into the net or not going in.”

Vella said Korn has stressed skating and footwork as any goalie coach does.

But Vella said Korn makes sure his messages are heard.

“He keeps adapting to the way the game is going,” Vella said. “He keeps learning and developing strategies to help guys. He comes at us every day with something new, something different, something we haven’t seen before. You just have to be a sponge and try to get as much as you can. It’s been fun to be able to pick the brain of a mind like that.”

The Islanders’ veterans report to training camp on Thursday and the first on-ice sessions are on Friday. Robin Lehner and Thomas Greiss enter camp expected to be the Islanders’ goaltending tandem.

Notes: The Islanders listed forward Michael Dal Colle, the fifth overall pick in 2014 who has four games of NHL experience, as day to day with a lower-body issue.