Common:Date Time Display Types

• As Entered - The date/time is stored and displayed exactly as entered.
• Convert to Local Date/Time - (Default) Value is presumed to be entered in user's local time zone. The value is converted to the System Time Zone for storage in the database. When displayed, it is converted the user's time zone.

Note:
These options are available for new fields in Custom Objects. They are not available for standard Date/Time fields (for example: modified_time) or for Date/Time fields in the System Objects. Those fields are always converted.