In the mobile we try to use the native calendar fields: http://www.w3schools.com/html/html5_form_input_types.asp
If this is supported by the browser then "date", "time" and "datetime" ar supported, but the display format is predefined by the browser, the format from the designer is only used to see what kind (date,time or datetime) should be used.
Servoy has a fallback build in if the native is not supported by the browser, if that fallback is hit, then the formats are used to display it, but the fallback has no support for "datetime", only for "date" and "time".
If you do want the fallback, because the native once are not working correctly (many samsung android phones at the moment) then you can override that the fallback should always be used. This can be done in 2 ways: