Unfortunately I don’t know a lot about UE4 networking. However, in both of these cases, it seems that you’d be better using reliable RPC to communicate to the server. No Timers or testing would be needed in this case.
For example, with the chat message, the player’s client sends the server a ChatMessage reliable event (Run on Server). The server can then play the sound at the player’s location.
Have a look at A Crash Course in Blueprint Replication. Hopefully that’ll help some.