Experience showed in Paragon and early Fortnite that “ping” from the beacon wasn’t super accurate because it was part of the tick loop of the engine. It could add up to 16ms @60fps on the client plus whatever time might be on the server if the tick processed actors just as the packet was received.
Have you looked at the ATestBeaconClient code that demonstrates how its the RPC that matters to start things off once the actor is spawned? The OnConnected() and other functions are meant to be internal details.
Apologies if this was already shared, but have you seen the docs I wrote up a few years ago after answering the original forum question?