In all Post calls, always use the UTC date format, 2015-12-11T09:00:00Z (i.e., include the trailing Z), to ensure correct creation of dates. In all cases, you should also declare the organizer's local time zone. This ensures the event displays in the organizer’s time zone in the Admin Center for GoToMeeting, GoToTraining, and GoToWebinar. These practices also result in consistent and correct treatment of dates in other APIs. If you omit either or both values, inconsistent behavior can result.

List of Time Zones