What is the average business time for Yelp_Business no.1 on weekends?
Yelp_Business no.1 refers to business_id = 1; on weekends refers to day_of_week = 'Saturday' or day_of_week = 'Sunday'; average business time refers to DIVIDE(SUBTRACT(closing_time, opening_time), 2)
SELECT T1.closing_time + 12 - T1.opening_time AS "avg opening hours" FROM Business_Hours AS T1 INNER JOIN Days AS T2 ON T1.day_id = T2.day_id WHERE T1.business_id = 1 AND (T2.day_of_week = 'Sunday' OR T2.day_of_week = 'Sunday')