It's a little complicated.
CNY & National Day Holidays have been the only two periods every movie have to start pre-sale at the same time since 2019. What happened in 2018 CNY helped the situation - Operation Red Sea began in ticket sale days later than other titles' selling due to slow processes. Film Administration, which took over from SARFT as film industry guardian in late 2018, decided to give all of them a same date. Therefore, pre-sale time is heavily dependent on their completions time and censorship processes. It wouldn't start soon if any movie couldn't be finished or get permission in time.
In 2019, films of CNY began selling its tickets in early January, 3.5 weeks before their dates. In 2020, things got a little out of control. The release of Leap, a sport project launched by Film Administration and The General Administration of Sport together, was opposed by former coach of Chinese women's volleyball team Chen Zhonghe. Chen believed the creative team did uglify him in this movie and used his influences in sport industry and public to stop its showing. Both administrations were forced to review it again and asked creative team to fix the problem. The censorship process of Leap led the beginning of CNY pre-sales to way later.
Some industry people also believe, Film Administration tended to cut the CNY pre-sale window in 2020 due to some controversies around distribution arguments between studios and exhibitors. Unlike the model in US film market, distribution talks are not very formal and promising especially no legal contract could be signed by any of them. So theaters and distributors could always break the unwritten deal if they have better plans to make money. Sometimes, it brought contradictions caused by different perceptions - everyone thought the other side is too unfaithful. In CNY, studios have to spend ¥100M-plus in marketing and distribution of one title. The risks suddenly become much higher in the happy festival. Film Administration think these conflicts could be reduced if the pre-sale window were short enough to make complicated appointments. But how short it should be? What 2020 CNY showed have made some people realize this method could be a killing hit to pre-sale and box office if only one(like DC3) is powerful enough to support the market.
CNY box office already showed danger signs considering admissions in the holidays of 2019 didn't increase from the same period of previous year. In terms of buzz and attention, the gap between DC3 and others is larger this year. If pre-sale come too late, pre-sale and daily gross could be weaker than usual. Too early? Nobody want to see fights as CNY is coming.