Is the time when the people's court finds the patent invalid the date of announcement, the date of decision or the date of receiving the decision? Or what?

When the people's court makes a judgment, if someone makes an invalid declaration, the court will generally wait until the announcement result of the Patent Reexamination Board comes out before making a judgment. Therefore, the time when the people's court finds the "invalid result" usually does not affect the rights and interests of the parties.

However, once the patent right is invalid, it is "regarded as nonexistent from the beginning". To put it bluntly, you should never put forward such a patent, and everything related to this patent should be restored to its original state. The whole right is gone, and it doesn't matter what date.

For example, if you implement the required technology after the patent application date, and then the patent is invalid, then you are not infringing. Of course, those implemented before the filing date are even less infringing.

I guess your focus is whether there is infringement, not its effective date.