高一牛津英语课文语法问题课本上有句话一直很纠结I was very happy with the school hour

高一牛津英语课文语法问题
课本上有句话一直很纠结
I was very happy with the school hours in Britain because school starts around 9 a.m and ends about 3.30p.m
这句话说,我想问为什么school starts around 9 a.m starts 后不加at?这句话的翻译应该是学校大约在9点上课,应该要加at啊,后句也一样,ends about 3.30p.m 在下午3点半放学 ,也应该加at啊,这两句是课本上的原话,表示有点不懂
另外,All the homework was in English 所有的作业都是英文的
这句话中,可否省略in 即 All the homework was English,省略以后,是否改变了原意?