I can't think of any new prototype plane that was A) flown without taxi tests and B) flown at night. I'm not saying it's impossible, but I can't think of any.
Usually, for any new type plane, and presumably especially for an expensive and crucial project like H-20, testing is done both slowly and methodically and carefully. So first there are taxi tests, when the plane is out in the open, but now flown. Those are done over a period of several months (not every day of course, but still on several/many occasions). Then the first flight test is done in the most careful and basic manner possible, under most controllable conditions. Usually it lasts a short time, is done during fair weather, and doesn't really involve anything. Often even the landing gear isn't retracted.
At the same time, this is 2022. Not only is the number of various cameras even bigger, but the number of possible low light and even night cameras is growing. Be it via night vision or thermal cameras. Truth to be told, that's all fairly inconsequential as I simply don't expect the first flight to be done at night time.
So once again, if the bomber is indeed being constructed in the Xi'an facility then I believe there is very little chance there won't be images appearing shortly after the plane gets outside. Given the AVIC promos over the years, I don't even think China will try to hide it at all.