My XML code sets StartTimeZone like this:
<t:StartTimeZone Id="Romance Standard Time"></t:StartTimeZone>
The value for Id I get from the Windows API GetTimeZoneInformation(). On my machine, I have tested setting the local time zone to just about everything, and the value I get works fine. For the example above, I had my local time zone in Windows set to "Brussels, Copenhagen, Madrid, Paris". A problem I just ran into is on one of my customers machines, running a French version of Windows 7 Pro, the value given by that API is "Paris, Madrid". EWS does not like this value for StartTimeZone. So I guess I just need to take the GMT offset I get and maintain my own table of valid EWS time zone strings. I can't seem to find that however - any ideas?