A bit weird that it also applies to weekends. I guess it helps not creating wrong incentives for companies, but it hurts open and personal projects a bit.
Quite simple. Chinese software companies rarely have true weekends. Most have alternating "Big/Small Weeks" (alternating between two days off and one day off) or just a single day off. This is the origin of the word "996" (working from 9 AM to 9 PM, 6 days a week) in the 996.icu movement initiated by Chinese programmers a few years ago.