How can I use TestService.SimulateSecondsLag to create artificial latency?

Trying to test the worst case scenario here.

Whether I run code that changes SimulateSecondsLag on the server, or the client, nothing changes. Does this only work in specific play testing situations? Like in-game, or in a test server?

I read somewhere else that someone tried using it with test server to no avail. It always takes ages for me to load up a test server, so I thought I’d ask here first.

I am not sure how to use TestService but

If you only want to stimulate lag another way is that you can change setting from File → Settings → Network → IncomingReplicationLag