都不对,正确的说法是twenty-four hours a day.
你们两种说法都没有说a day, 是有歧义的. it opens 24 hours a week也可以啊.
The opening hours是说营业时间,一般都用从几点到几点的表达,is from 8am to 10pm.
The opening hours是24小时,我表示你们老师水平不高.
便利店就巨头7-eleven的说法就是 "opens 24 hours a day, 7 days a week"