Setting a date/time value to a date/time workflow variable outputs the wrong time at workflow execution.

This is by design. SharePoint will adjust the time stored in the workflow variable to GMT (UTC+0), plus add time to account for daylight savings. SharePoint does not know the time zone of the date/time value being saved to the workflow variable, so the time is adjusted based on regional settings when used in a workflow. We recommend using the "Add Time to Date" action to adjust the date/time workflow variable to the correct time.