When the User signs up tabUp tries to set a default location in the Users profile.  If we are unable to do this it defaults to Stamford, Connecticut, U.S.    The timezone will also be set to Eastern, U.S.     A User can correct the timezone setting in their Profile > Preferences page. 

So, if you put a calendar appointment in your tab, users with the wrong timezone defined will see the event adjusted to their defined timezone.  I believe this is the cause of incorrect email event times, they are probably also incorrect when the user is logged in to tabUp.   

If you have the members of your tab check their preference it should correct the problem.

User Dashboard > My Profile > My Preferences