Write SQL query to solve given problem: What is the average business time for Yelp_Business no.1 on weekends?. Keep the solution inside sql tag ```sql [SQL-Query] ```
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')