How to use a countdown timer for one page server only for (2 :55)

Question

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Timer ID="Timer1" runat="server" Interval="1000" OnTick="Timer1_Tick">
</asp:Timer>
<asp:Label ID="Label1" runat="server" Text=""></asp:Label>
</ContentTemplate>
</asp:UpdatePanel>

protected void Page_Load(object sender, EventArgs e)
{
if (Session["CountdownTimer"] == null)
{
Session["CountdownTimer"] = new CountDownTimer(TimeSpan.Parse("00:02:55"));
(Session["CountdownTimer"] as CountDownTimer).Start();
}
}
protected void Timer1_Tick(object sender, EventArgs e)
{
if (Session["CountdownTimer"] != null)
{
Label1.Text = (Session["CountdownTimer"] as CountDownTimer).TimeLeft.ToString();
string GetTime = Label1.Text;
string[] Array = GetTime.Split(':');
string Minutes = Array[1];
string Seconds = Array[2];
if (Convert.ToInt32(Minutes) == 00 && Convert.ToInt32(Seconds) == 30)
{
//boxid.Enabled = false;
//boxid.ReadOnly = true;
}
else if (Convert.ToInt32(Minutes) == 0 && Convert.ToInt32(Seconds) == 0)
{
Session["CountdownTimer"] = new CountDownTimer(TimeSpan.Parse("00:02:55"));
(Session["CountdownTimer"] as CountDownTimer).Start();
//boxid.Enabled = true;
//boxid.ReadOnly = false;
}
}
}
public class CountDownTimer
{
public TimeSpan TimeLeft;
System.Threading.Thread thread;
public CountDownTimer(TimeSpan original)
{
this.TimeLeft = original;
}
public void Start()
{
// Start a background thread to count down time
thread = new System.Threading.Thread(() =>
{
while (true)
{
System.Threading.Thread.Sleep(1000);
TimeLeft = TimeLeft.Subtract(TimeSpan.Parse("00:00:01"));
}
});
thread.Start();
}
}

I am using this code but it is not working according to my requirement.

 

My Requirement the countdown timer for eg:- Timer is open 10 devices and 20 devices(mobile and laptop from differenr I.P.). the timer is same all the time. run only 2 minute 55 second (5 second pause) is it possible so please help me (ASP.NET C#)