For it to be the safest and most efficient without down the game, should I code it all on the server then update everyone's clock(Player Gui) individually from the server via a for loop?
Or should the server have a uniform clock value that's constantly changing, and the client updates it's own gui every second by communicating with the server?

2 comments
have an int value in replicated storage, change it on the server and get it on the client
The king, wouldn't that be bad because leaving the int value in replicated storage could leave it open for hackers?