Quoting the page you linked:
The server needs to know the time zone of each user. Unfortunately, the web browser cannot report this information. It only reports the current offset to UTC. This is not enough to determine the exact time zone and properly deal with daylight saving time of future and past dates. For this reason web applications often offer you the option of setting your time zone and we have now built this option into Mendix, too. You can explicitly set a time zone for each user and this time zone is then used for server operations.
This is an important detail. The client will always use the webbrowser's timezone (or UTC) for displaying dates, unfortunately this is not something we can influence. It's recommended to let your users set their timezone to the actual timezone their computer is set to.