This is what I figured out for my own project. I drew over the irrelevant game specific nodes, but the rest should work for everyone. The delay is in no way determined in a scientific way, it’s just a rough guess of when the grass would have spawned in. The component I am getting in the “GetComponentsByClass” is “GrassInstancedStaticMeshComponent”.
It was just a bunch of work to figure this out, so this is for anyone (and myself) who happens to google changing landscape materials at runtime or changing landscape grass materials at runtime in blueprint to be specific.