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

protected void Page_Load(object sender, EventArgs e)
{
   System.Threading.Thread.Sleep(100);
   string currenttime = DateTime.Now.ToLongTimeString();
   lblcurrenttime.Text = currenttime;
}