I have a deployment where they were setup with using the server time zone for all Citrix Sessions. 1 PVS server suddenly came up on the wrong coast. Digging through the event logs we found that Outlook changed the entire servers time zone from a user session. This is explicitly disabled via policies so that only admins and system could do this. We fired up our test environment, and used our regular test account and look at that, changing time zones in outlook calendar options changed the whole server.
To fix this we enabled client side time zone redirection in GPO for RDS and Citrix Studio Policies. Then when users logged in it picked up the client time zone, and changed the time zone inside of outlook calendar to the other coast, but only for that user session, not for the entire server.
Still digging through why Outlook would be able to override system restrictions to set the server time zone as the user.