State the full name of clients with server time of 20 minutes and above.
full name refers to first, middle, last; server time of 20 minutes and above refers to ser_time > '00:20:00'
SELECT T1.first, T1.middle, T1.last FROM client AS T1 INNER JOIN callcenterlogs AS T2 ON T1.client_id = T2.`rand client` WHERE strftime('%M', T2.ser_time) > '20'