Hello Paul,
This check is not about the users timezones but the server itself. The auth token has an expiration time and a refresh time. If the servers time is off by too much it breaks the calculation and the refresh fails. This check is all local to the server and does not touch the users tine or timezones.
Hope this helps to clarify the issue.
Thank you
Tony Scholz
System/Network Administrator
SmarterTools Inc.
www.smartertools.com