SELECT t.*, q.*, ( LEAST(t.e1, q.e2) - GREATEST(t.b1,q.b2) ) *24*60 AS dur
FROM 
(SELECT TO_DATE('01.10.20 08:01:00') AS b1
      , TO_DATE('01.10.20 08:06:00') AS e1 
 FROM dual
) t 
JOIN (SELECT TO_DATE('01.10.20 08:00:00') AS b2
           , TO_DATE('01.10.20 08:10:00') AS e2 FROM dual 
      ) q ON q.b2 < t.e1
         AND q.e2 > t.b1
         AND ( LEAST(t.e1, q.e2) - GREATEST(t.b1,q.b2) ) *24*60*60 >= 30