How to automatically close gui after 4 seconds?!

Im making a murder mystery type game and i have guis to display the role of the player when the round starts. The game is locked in first person so i cant add a button and i want it to automatically close after 4 seconds. however, everything i try wont work. here is my code:

local killerWeapon = game.ServerStorage.Knife
local plrs = game.Players
local inRound = game.ReplicatedStorage.inRound

local survivors = {}


inRound.Changed:Connect(function()
	if inRound.Value == true then
		local chosen = plrs:GetChildren()[math.random(1, #plrs:GetChildren())]	

		chosen.PlayerGui.Picker.Background.RoleGiven.Text = "Murderer"
		chosen.PlayerGui.Picker.Background.RoleGiven.TextColor3 = Color3.fromRGB(255, 0, 0)

		chosen.PlayerGui.Picker.Background.Visible = true

		killerWeapon:Clone().Parent = chosen.Backpack
		print("killer")
		
		
		


		for i, plr in pairs(plrs:GetChildren()) do

			if plr ~= chosen then

				table.insert(survivors, plr)

				plr.PlayerGui.Picker.Background.RoleGiven.Text = "Survivor"
				plr.PlayerGui.Picker.Background.RoleGiven.TextColor3 = Color3.fromRGB(0, 255, 0)

				plr.PlayerGui.Picker.Background.Visible = true
				print("survivor visible")

			end	
		end	
	end	
end)

When looping through players, consider adding a coroutine if you're waiting for a specific period of time.

A coroutine creates a new thread & allows the environment to continue running without yielding; this is what we call Multithreading.

local PlayersService = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local ServerStorage = game:GetService("ServerStorage")

local BoolValue = ReplicatedStorage:WaitForChild("inRound")
local Knife = ServerStorage:WaitForChild("Knife")
local Survivors = {}

ReplicatedStorage:WaitForChild("inRound").Changed:Connect(function(property)
	if tostring(property) == "Value" then
		local inRound = BoolValue.Value
		if inRound == true then
			local Chosen = PlayersService:GetPlayers()[math.random(1, #PlayersService:GetPlayers())]
			local PlayerGui = Chosen:FindFirstChildWhichIsA("PlayerGui") or Chosen:WaitForChild("PlayerGui")

			local Picker = PlayerGui:WaitForChild("Picker")
			local Background = Picker:WaitForChild("Background")
			local RoleGiven = Background:WaitForChild("RoleGiven")

			RoleGiven.Text = "Murderer"
			RoleGiven.TextColor3 = Color3.fromRGB(255, 64, 64)

			coroutine.wrap(function()
				wait(4)
				Background.Visible = false

				local BackpackItem = Knife:Clone()
				BackpackItem.Name = "Knife"
				BackpackItem.Parent = Chosen:FindFirstChildWhichIsA("Backpack") or Chosen:WaitForChild("Backpack")
			end)()

			pcall(print, Chosen:GetFullName() .. " is now the suspected killer.")

			for _, Player in pairs(PlayersService:GetPlayers()) do
				if Player ~= Chosen and Player.Character and typeof(Player.Character) == "Instance" and Player.Character:IsDescendantOf(workspace) then
					local Humanoid = Player.Character:FindFirstChildWhichIsA("Humanoid")
					if Humanoid:GetState() ~= Enum.HumanoidStateType.Dead and Humanoid.Health > 0 then
						table.insert(Survivors, Player)
						local PlayerGui = Player:FindFirstChildWhichIsA("PlayerGui") or Player:WaitForChild("PlayerGui")

						local Picker = PlayerGui:WaitForChild("Picker")
						local Background = Picker:WaitForChild("Background")
						local RoleGiven = Background:WaitForChild("RoleGiven")

						RoleGiven.Text = "Victim"
						RoleGiven.TextColor3 = Color3.fromRGB(64, 255, 64)

						coroutine.wrap(function()
							wait(4)
							Background.Visible = false
						end)()

						pcall(print, Player:GetFullName() .. " is a victim of the suspected killer.")
					end
				end
			end
		end
	end
end)

Just add a wait()...??

-- between lines 37 and 38 maybe
wait(4)
for i, plr in pairs(plrs:GetChildren()) do
	plr.PlayerGui.Picker.Background.Visible = false
end