Is it serious for Huahai Zhihui to work overtime?

Nothing serious. According to the recruitment website Zhiyouji, Huahai Zhihui doesn't have to work overtime, occasionally. The full name of the company is Huahai Zhihui Technology Co., Ltd., formerly known as Huawei Ocean Network Co., Ltd., which is a joint venture between Huawei Technologies Co., Ltd. and Global Ocean Systems Co., Ltd. Relying on the advantages of their respective parent companies, Huawei Ocean is committed to building a global submarine optical cable communication network by combining the most advanced technology in the communication industry and more than 160 years of marine construction experience.