The default time zone setting that is displayed in the Preferences>General folder is used to localize the time for received messages and calendar activities in the standard web client.
When using the standard web client, the time zone on the computer is not used to set the time a message is received or for calendar activities; the time zone setting in the Preferences>General tab is. However, when using the advanced web client, the time zone setting on the computer is used to as the time stamp for received messages and for calendar activities, not the time zone setting on the General tab.
Note: Because the advanced web client and the standard web client do not use the same time zone source to render messages, you may notice that the same message has a different time when displayed in one or the other client. You can avoid this by having the computer time zone and the web client time zone set to the same time.