For the event which happened at 23:33:34 on 2016/5/6, how many installed apps were involved?
at 23:33:34 on 2016/5/6 refers to timestamp = '2016/5/6 23:33:34'; installed refers to is_installed = '1';
SELECT COUNT(T1.event_id) FROM app_events AS T1 INNER JOIN events AS T2 ON T1.event_id = T2.event_id WHERE SUBSTR(T2.`timestamp`, 1, 10) = '2016-05-06' AND T1.is_installed = '1'