WHEN DATEDIFF(MINUTE,a.start_time, a.end_time) > 60
                    THEN CAST(DATEDIFF(MINUTE,a.start_time, a.end_time) / 60 AS VARCHAR(20)) + ' ' + N'ч.' + CAST(DATEDIFF(MINUTE,a.start_time, a.end_time) % 60 AS VARCHAR(20)) + ' ' + N'мин.'
                  ELSE CAST(DATEDIFF(MINUTE,a.start_time, a.end_time) AS VARCHAR(20)) + ' ' + N'мин.'
                END