require('timers')

...the rest of your code

//this function happens when the clock counts down to zero and the game begins
function GameMode:OnGameInProgress()
  print("[BAREBONES] The game has officially begun")

  //this is the actual line to create a timer
  Timers:CreateTimer(30, -- Start this timer 30 game-time seconds later
  function()
    print("This function is called 30 seconds after the game begins, and every 30 seconds thereafter")
    return 30.0 -- Rerun this timer every 30 game-time seconds
  end)
end