SELECT t1.id, SUM(TIMESTAMPDIFF(SECOND, t2.Update_time, t1.Update_time)) 
FROM source t1
INNER JOIN source t2 ON t1.id=t2.id 
                    AND t2.Update_time>t1.Update_time 
                    AND t2.Status='pending'
LEFT JOIN source t3 ON t1.id=t3.id 
                    AND t3.Update_time>t1.Update_time 
                    AND t2.Update_time>t3.Update_time 
                    AND t3.Status='pending'
WHERE t1.Status='done'
  AND t3.id IS NULL
GROUP BY t1.id

WITH 
cte AS ( SELECT *, 
                LEAD(Status) OVER (PARTITION BY id ORDER BY Update_time ASC) nStatus,
                LEAD(Update_time) OVER (PARTITION BY id ORDER BY Update_time ASC) nUpdate_time
         FROM source
         WHERE Status IN ('pending','done') )
SELECT id, SUM(TIMESTAMPDIFF(SECOND, Update_time, n.Update_time)) 
FROM cte
WHERE Status='done'
  AND nStatus='pending'
GROUP BY id