One of the major disadvantages is that the shopkeepers would have to work [until] midnight or perhaps on bank holidays.

shopkeepers 是由 shop（商店）和 keeper（看守者、管理者）组成的复合词，字面意思是"商店看守者"，即"店主"。 until 是介词，表示"直到...时候"，用来指明动作或状态持续到某个时间点。 bank holidays 是固定短语，bank 指"银行"，holiday 指"假日"，在英国和部分英联邦国家特指"法定公共假日"。