What is the opening time of the active businesses in Chandler that has a medium review count.
active businesses refers to active = 'true'; in Chandler refers to city = 'Chandler'
SELECT DISTINCT T2.opening_time FROM Business AS T1 INNER JOIN Business_Hours AS T2 ON T1.business_id = T2.business_id INNER JOIN Days AS T3 ON T2.day_id = T3.day_id WHERE T1.city LIKE 'Chandler' AND T1.active LIKE 'TRUE' AND T1.review_count LIKE 'Medium'