The Force.com Calendar displays a calendar and has a Guess Site User assigned to it.
CalendarAnything displays the current time for Day View and for Swimlane View. This is loaded from the User’s Time Zone in the Settings. In order to configure this all you have to do is:
Go to Setup
In the Quick Find type “Site”
Click on “Sites”
Locate your Force.com site and click on site label to open site details
Click on Public Access Settings button
Click on Assigned Users button
Click on Edit next to the site guest user name
Change the Time Zone to your desired one
Now your Force.Com calendar will change its time zone.