AppointmentItem.StartTimeZone Property (Outlook)
Returns or sets a TimeZone value that corresponds to the time zone for the start time of the appointment. Read/write.
The time zone information is used to map the appointment to the correct UTC time when the appointment is saved, and into the correct local time when the item is displayed in the calendar.
Depending on the circumstances, changing the StartTimeZone may or may not cause Outlook to recalculate and update the AppointmentItem.StartInStartTimeZone.
As an example, in the appointment inspector, if you are the organizer of an appointment with a start time at 1 P.M. PST and end time at 3 P.M. PST, changing the appointment to have an StartTimeZone of EST will result in an appointment lasting from 1 P.M. EST to 3 P.M. PST, with the StartInStartTimeZone remaining as 1 P.M. However, if you are not the organizer, then changing the StartTimeZone from PST to EST will cause Outlook to recalculate and update the StartInStartTimeZone, and the appointment will last from 4 P.M. EST to 3 P.M. PST.
Another example is changing the StartTimeZone resulting in an appointment end time that occurs before a previously set appointment start time, in which case Outlook will recalculate and update the StartInStartTimeZone. For example, an appointment with a start time at 1 P.M. EST and end time at 3 P.M. EST has its StartTimeZone changed to PST. If Outlook did not recalculate the StartInStartTimeZone, the appointment would have a start time at 1 P.M. PST, which is equivalent to 4 P.M. EST, and which would occur before the end time of 3 P.M. EST. In practice, however, changing the StartTimeZone would result in Outlook recalculating and updating the StartInStartTimeZone to 10 A.M. (in the StartTimeZone PST).