The Account time zone is used for displaying monthly usage, as well as message scheduling and reporting send-time references. It also comes into play when you use the socially aware sending option to restrict your message sending to a window of sociable hours.
To change the account time zone:
1. Go to Account > Account Settings
2. Click on the Edit icon next to "Account time zone":
3. Use the dropdown menu to locate the required time zone:
4. Click Save