To reproduce:
- Add GridViewDateTimeColumn.
- Set the editor properties:
private void radGridView_VehicleAbsenceTime_CellEditorInitialized(object sender, GridViewCellEventArgs e)
{
    RadDateTimeEditor lEditor = radGridView_VehicleAbsenceTime.ActiveEditor as RadDateTimeEditor;
    if (lEditor != null)
    {
        RadDateTimeEditorElement editorElement = (RadDateTimeEditorElement)lEditor.EditorElement;
        editorElement.Format = DateTimePickerFormat.Custom;
        editorElement.CustomFormat = "dd.MM.yyyy HH:mm";
        editorElement.ShowUpDown = true;
    }
}
- Start the application scroll to the bottom and start editing.