Hi Sofia!
When I think of character meals for a boy, a meal with Mickey and Donald generally come to mind!
Chef Mickey's at the Contemporary Resort feature Mickey, Donald, Minnie, Goofy, and Pluto! Both my children (ages 6 and 2) enjoyed this restaurant!
Donald's Safari Breakfast at Tusker House (Animal Kingdom) also feature the Disney Fab Five.
The Crystal Palace at Magic Kingdom (Main Street) feature Winnie the Pooh, Tigger, and Friends.
Hollywood and Vine at Hollywood Studios feature Playhouse Disney characters such as the Little Einstein's.
Not character dining, but a family favorite is the Coral Reef restaurant at Epcot, which features an enormous aquarium where you can see sharks, stingrays, etc. My son loved this restaurant!
As for time, I would say on average 1 hour 15 minutes-1 hour 30 minutes from the time you're seated to walking out for character meals. The food generally comes out reasonably fast, but you'll stop a few minutes to take pictures for each character, as they hit tables one character at a time.
Have the most magical of times on your first Disney trip!