Mr. R.’s World of Math

Finally Irving said, “I don’t know how the birthmark took its form, but facts are facts! Now I need to find a Matthew with the Mark of the Martian Matthew on their left knee.”
I noticed that Matthew, who wore short pants every day of the year (yes, even the coldest ones) put his hands over his knees.
At this point, Irving noticed the name labels I’d put on the students’ desks. He saw the label that said Matthew.
“Matthew?” asked Irving, “Your name is Matthew?”
“Y-y-y-yess,” stammered Matthew who was definitely scared now.
“Leave Matthew alone. He has nothing to do with Mars chocolate or broccoli, or any of your nonsense!” said Anthony.
“Please stand up, Matthew,” said Irving.
“Hey,” I cried, “Don’t you dare make my students do things without my or their permission.”
“Be quiet, Earthling!” yelled Irving, who suddenly was angry. “I will find the descendants of the person who turned our famous Mars chocolate into broccoli, and nobody’s going to stop me!” Then he tapped a device he was wearing on his wrist, and we all froze in place like statues.
We could only watch as Irving pointed his finger at Matthew. We were shocked to see that Matthew slowly began floating out of his seat. Matthew levitated in mid-air, in front of Irving and Irving slowly reached out and pulled on Matthew’s left foot until his leg was straight. He looked directly at Matthew’s knee.
Irving saw it, we all saw it and we were all shocked that we’d never noticed it before. 
There was a birthmark that was the shape of an avocado flying with a parachute. It was unmistakable.
Irving laughed, and said, “I’ve found you on the first try. I knew I would! You’re coming back to Mars, and you will stay there until you figure out how to turn all the broccoli back into chocolate!” And then Irving waved his hands wildly as the million pieces of ‘rock’ on the floor flew up into the air and formed into a spaceship.
A ramp lowered down from the spaceship and Irving dragged Matthew into the spaceship like a balloon floating on a string. The ramp retracted into the bottom of the ship and  a door started to close.  Just before it closed, Irving said,
“So long, class!” and he pushed the button on his device that unfroze us.

If Irving had appeared in the classroom at 8:48, and the door of the spaceship closed at 10:17, how many MINUTES had passed?