1. "Enable Timezone Conversions" needs to be set to "Yes" at the Site level.
2. "Server Timezone" needs to be set at the Site level to the timezone in which the database server resides.
3. "Client Timezone" needs to be set for each individual user at the User level based on the users physical location (not setting this at the User level will default the value to the "Server Timezone" value).
For personalizations, pl see MOS Doc 304670.1 (How to Remove an OA Framework Personalization)
How Should The Client Time Zone And Session Timezone Be Set Up By The User From The Display Preferences Screen in Personalization Section In OSO? [ID 219316.1]
User Preferred Time Zone Support Guidelines for Applications 11i10CU2 [ID 330075.1]