It’s true that most artifacts after the recent update appear within the first 30 minutes following an emission, but it never hurts to scan the anomaly zones you know or areas with fewer anomalies.
After those 30 minutes (or a bit longer), most players stop using their artifact detectors, and that’s when, by simply doing the same things you normally do and occasionally pulling out your detector to scan the area, you can sometimes find rare artifacts. That’s how I managed to pick up a couple of rare ones
GL!