I created a custom Entity with one of the properties named 'created' and set with the Drupal
REQUEST_TIME in seconds. I want to display this property using the Views module as a formatted Date/Time field. The Date/Time format option is not offered on the Views field settings dialogue.
hook_entity_property_info_alter() to describe your custom entity type's properties to the Entity API module, which will then automatically create Views integration based on the types of fields in your database table.
An example of this can be found in the Log module, which has three timestamps (timestamp, created, and changed). It gives each of these a "type" of "date" in the entity property info, which automatically makes them visible to Views as date fields. http://cgit.drupalcode.org/log/tree/log.module#n242