There is no set schedule. The buses, boats, and monorail are "continuous" from about 90 minutes before park opening till about 90 minutes after park closing.
Near opening and closing they have more buses, so they come more frequently, during the middle of the day, they are more space apart as there are fewer buses.
From park to park is as follows:
Magic Kingdom to Epcot: - Monorail - transfer at TTC, Monorail
Magic Kingdom to Studios - Monorail to TTC, bus to Studios
OR
Walk to Contemporary (5 minutes), bus to Studios
Magic Kingdom to Animal Kingdom - Monorail to TTC, bus to Animal Kingdom
OR
Walk to Contemporary, bus to Animal Kingdom
Epcot to Magic Kingdom - Monorail - transfer at TTC, Monorail
Epcot Future World to Studios - Direct Bus
Epcot World Showcase to Studios - Boat or Walkway
Epcot to Animal Kingdom - Direct Bus
Studios to Magic Kingdom - Bus to TTC, Monorail
OR
Bus to Contemporary, walk
Studios to Epcot Future World - Direct Bus
Studios to Epcot World Showcase - Boat or Walkway
Studios to Animal Kingdom - Direct Bus
Animal Kingdom to Magic Kingdom - Bus to TTC, Monorail
OR
Bus to Contemporary, Walk
Animal Kingdom to Epcot - Direct Bus
Animal Kingdom to Studios - Direct Bus