How many business have low check-in on Sunday at 10AM?
on Sunday refers to day_of_week = 'Sunday'; low check-in at 10AM refers to label_time_10 = 'Low'
SELECT COUNT(T2.business_id) FROM Days AS T1 INNER JOIN Checkins AS T2 ON T1.day_id = T2.day_id WHERE T1.day_of_week = 'Sunday' AND T2.label_time_10 = 'Low'