How can i make a timed click to +1 leaderstats?

If this is a tool in a local script, you'll have to use a RemoteEvent to tell the server to update the leaderstat as changes you make on the client will not replicate to others. Nevertheless, here is what you requested. Assuming your code is on the server, you will need to add a debounce for each player to determine when they can click again. This can be done with a BoolValue.

script.Parent.Activated:Connect(function() 
	local char = script.Parent.Parent 
	local plr = game.Players:GetPlayerFromCharacter(char)

	local debounce = char.Debounce or Instance.new("BoolValue", char)
	debounce.Name = "Debounce"

	local leaderstats = plr:FindFirstChild("leaderstats")
	if leaderstats and debounce.Value == false then 
		debounce.Value = true
		local coins = leaderstats:FindFirstChild("Cash")
		local boost = plr:FindFirstChild("CoinBoost") 
		if coins and boost then 
			coins.Value = coins.Value + 1 + boost.Value 
		end 
		wait(1) --Change to cooldown
		debounce.Value = false
	end 
end)