From their website:

"Do anomalies have an expiration date?

Theoretically, no. The MMI effect is designed to generate data that will lead to positive observation. And since this positive observation has already happened, it does not matter when you visit the point. However, we do not have any accurate data confirming this, so check for yourself.

Is it possible to generate the same point twice? Is it possible for someone else to generate a point you generated?

In theory, IDAs have been stable for some time when your thought has an impact on the RNG. Therefore, it is quite possible that several attempts to generate a point will find the anomaly in the same place. If several users influence the RNG at the same time, it is possible that their intentions will be mixed, but there is no data confirming this yet, so try to find out for yourself."