I agree with the previous poster. The scavenger hunts can take as little or long as you want them to. Also, Agent P's in Epcot is a different hunt in each of the offered countries.
Here's some of mine:
AK-If you have children, head to The Boneyard. The kids all like the huge play area & dig for dinosaur bones.
EP-Pick A Pearl in Japan. Churros in Mexico.
MK-Silhouette pictures in Liberty Square, Christmas Ornaments in Liberty Square, Ferry Boat ride, Tom Sawyer's Island, Train Ride around the park, Peoplemover, Tomorrowland Speedway
HS-Muppets, Art of Animation
All parks-We also like searching for pressed penny machines in the parks, hidden Mickey's.