I read that December 23rd was when the virus was first noted as novel and spreading, and Hubei closed down January 23rd. That’s a little over 4 weeks, with a brand new virus that they certainly didn’t have the data then that we have now.
As you very well know, closing down a province that has a larger population than California couldn’t be taken lightly with the limited information they had then, and WHO had even commended China on its swift response.
I am by no means saying that China’s censorship and suppression aren’t problematic (they very well are), but in this case you’re looking at the situation with 20/20 vision, with the knowledge you possess two months after Hubei’s closure.
By contrast, when this virus entered our shores on January 21st, it wasn’t until 2 months later that states started sheltering in place, and there still aren’t any wholesale traveling restrictions (at least that I’m aware of).