Server to client communication

Not sure what heading this would fall under, but what I’m wanting to do is to have the clients run a timer locally on their side, preferably synced with the main server, then have each of these timers collect the amount of time it takes for each client to react with a button press. I then want a “Blackout” or “deciding” screen which involves the clients telling the server how long locally it took to push the button, then the server decides the winner from this information.

I’m pretty early on in development for the game I’m working on so I have no “examples” to show, but basically I want to remove the server lag in a chance based game.

Thanks to anyone that can help.