In a 4 cluster multi-cluster deployment (1 hub + 3 managed clusters) with 10 nodes in each managed cluster we see that service exports take 3 to 6 hours to be discovered by another clusters (i.e see the corresponding service exports).
In the above scenario we are creating 1900 services backed by 1900 pods on one of the managed clusters. (say cluster0)
It took 3 hours to see all the 1900 services in cluster1.
After sometime I created the same namespace on another cluster (cluster2) to see how much time it takes to see all the service imports. This time it took around 6 hours.

Classic ROSA 4.15.8    

    1. Described above

Service discovery in client cluster takes 3-6 hours    

The service discovery time should be much shorter