By default, the calendar will return all shows or movies for the specified time period and can be global or user specific. The start_date defaults to today and days to 7. The maximum amount of days you can send is 33. All dates (including the start_date and first_aired) are in UTC, so it's up to your app to handle any offsets based on the user's time zone.
The my calendar displays episodes for all shows that have been watched, or watchlisted plus individual episodes on the watchlist. It will remove any shows that have been hidden from the calendar. The all calendar displays info for all shows airing during the specified period.