Shares in Chinese technology firms have fallen after the country’s online regulator announced plans recommending smartphone use for children be limited to a maximum of two hours a day. The rules proposed by the Cyberspace Administration of China (CAC) will require device makers, operating systems, apps and app stores to introduce a so-called “minor-mode” capping time spent on screens, increasing the pressure on local tech companies already grappling with tight government controls. The proposals, which are still subject to public feedback, would limit users aged 16-18 to two hours usage…