How can I add a countdown timer for the game to end?

So I made a mini game script that works well, but the problem is, I do not know how to add a countdown timer. Because both players (f1, and f2) could be moving around not shooting nothing each other then game will never end, basically if a player dies or a player leaves, then the other player would get the victory and the game would end. Didn't want to put whole script having you look line to lines, so I added the main part. Usually the game does not end until someone dies or someone leaves, but I want to add a timer to end the game once it hits 0. Appreciate it!

    --Script by Apex
Spawn1 = Vector3.new(-18.9, 6.91, -12.669) -- where to spawn Stone cold
Spawn2 = Vector3.new(-18.9, 6.91, 20.814) -- where to spawn Kane
mTime = 3 -- ammount of time for messages to appear
winner = nil
stat = "wins" -- name of the leaderstat to add points too
points = 1 --the number to give to the above stat ^
intermission = true -- if you don't want an intermission then set to false
interTime = 30-- the intermission length if you have one
SS = game:GetService("Lighting")
local weapons = game.ServerStorage.Weapons:GetChildren()
---------------------------------------------------------------------
local Players = game:GetService("Players")
local replicatedstorage = game:GetService("ReplicatedStorage")
local m = replicatedstorage:WaitForChild('InfoValue')
local l = game.ServerStorage
workspace.Int2:Play()
while wait() do
    repeat 
        wait() 
        m.Value = "2 or more players needed to start."
    until game.Players.NumPlayers >=2
    local m = replicatedstorage:WaitForChild('InfoValue')
    repeat 
    wait() 
    m.Value = "2 or more players needed to start."
    until game.Players.NumPlayers >=2

    if intermission then
        workspace.Int2:Stop()
            wait(0.1)
            workspace.Music:Play()
        for i = interTime,1,-1 do
            m.Value = "Intermission - "..i
        end
    end
    m.Value = "Choosing a random player..."
    wait(mTime)
    local pl = game.Players:GetPlayers()
    for i = 30,1,-1 do
        wait(i*0.04)
        m.Value = pl[math.random(1,#pl)].Name.." vs "..pl[math.random(1,#pl)].Name
    end
    f1 = pl[math.random(1,#pl)]

    repeat wait() -- avoid the same player fighting themself :P
    f2 = pl[math.random(1,#pl)]
    until f2 ~= f1
    wait(mTime)
    m.Value = f1.Name.." VS "..f2.Name.."!"
    wait(0.1)
    f1.PlayerGui.SpectateGui:Destroy()
    wait(0.1)
    f2.PlayerGui.SpectateGui:Destroy()
    wait(mTime)
    m.Value = "GET READY! KNIFE FIGHT"
    wait(mTime)
    m.Value = "Spawning players..."
    wait(1)
    f1.Character.Humanoid.WalkSpeed = 0
    wait(0.1)
    f1.Character.Humanoid.Jump = true
    wait(0.3)
    f1.Character:MoveTo(Spawn1)
    wait(1)
    f2.Character.Humanoid.WalkSpeed = 0
    wait(0.1)
    f1.Character.Humanoid.Jump = true
    wait(0.3)
    f2.Character:MoveTo(Spawn2)
    wait(1)
    workspace.Music:Stop()
    workspace.St:Play()
    game.ServerStorage.Sto:Clone().Parent = game.Workspace
    for i,v in pairs(game.Players:GetPlayers()) do
        local cs1 = SS.CutsceneScript3:Clone()
        v:WaitForChild("Backpack")
        cs1.Parent = v.Backpack
        cs1.Disabled = false
    end
    wait(14)
    workspace.St:Stop()
    m.Value = "Let's start the introduction.."
    wait(4.4)
    m.Value = "Ladies and Gentleman! Make some noise for "..f1.Name.."!!"
    wait(0.2)
    for i,v in pairs(game.Players:GetPlayers()) do
        local cs1 = SS.CutsceneScript:Clone()
        v:WaitForChild("Backpack")
        cs1.Parent = v.Backpack
        cs1.Disabled = false
    end
    wait(0.1)
    game.Workspace.Crowd:Play()
    wait(5.1)
    game.Workspace.Crowd:Stop()
    wait(2)
    m.Value = "Ladies and Gentleman! Make some noise for "..f2.Name.."!!"
    wait(0.2)
    for i,v in pairs(game.Players:GetPlayers()) do
        local cs1 = SS.CutsceneScript1:Clone()
        v:WaitForChild("Backpack")
        cs1.Parent = v.Backpack
        cs1.Disabled = false
    end
    wait(0.1)
    game.Workspace.Crowd:Play()
    wait(5.1)
    game.Workspace.Crowd:Stop()
    wait(2)
    m.Value = f1.Name.." and "..f2.Name.." you better get to know each other before yall fight..."
    wait(3)
    workspace.Int:Play()
    wait(20)
    m.Value = "TIP: Take your time shooting and use it wisely, so that you do not run out of ammo."
    workspace.Int:Stop()
    wait(3)
    game.Workspace.Buzz:Play()
    m.Value = "3"
    wait(1)
    game.Workspace.Buzz:Play()
    m.Value = "2"
    wait(1)
    game.Workspace.Buzz:Play()
    m.Value = "1"
    wait(1)
    game.Workspace.Go:Play()
    workspace.Sto:Destroy()
    m.Value = "FIGHT!!!"
    wait(1)
    f1.Character:MoveTo(Vector3.new(-155.5, 6.91, -125.2))
    wait(0.1)
    f2.Character:MoveTo(Vector3.new(109.8, 6.91, 137.502))
    wait(0.1)
    local random = weapons[math.random(1, #weapons)]
    random:Clone().Parent = f1.Backpack
    l["Smoke Grenade"]:Clone().Parent = f1.Backpack
    wait(0.1)
    random:Clone().Parent = f2.Backpack
    l["Smoke Grenade"]:Clone().Parent = f2.Backpack
    f1.Character.Humanoid.MaxHealth = 300
    f1.Character.Humanoid.Health = 300
    f1.Character.Humanoid.WalkSpeed = 16
    wait(0.1)
    f2.Character.Humanoid.MaxHealth = 300
    f2.Character.Humanoid.Health = 300
    f2.Character.Humanoid.WalkSpeed = 16
repeat
        wait()
         if not Players:FindFirstChild(f1.Name) or (f1.Character.Humanoid.Health <= 0)  then 
        winner = f2

    elseif not Players:FindFirstChild(f2.Name) or (f2.Character.Humanoid.Health <= 0) then 
        winner = f1
    end
until winner ~= nil
    if winner:findFirstChild("leaderstats") then
        if winner.leaderstats:findFirstChild(stat) then
            winner.leaderstats[stat].Value = winner.leaderstats[stat].Value + 1
        end
    end
    m.Value = "The winner is... "..winner.Name.."!"
    wait(1)
    game.Workspace.Crowd1:Play()
    wait(10)
    game.Workspace.Crowd1:Stop()
    wait(1)
    winner.Character:BreakJoints()
    winner = nil
end