I have refer your code its get executed in every 1000 mili-seconds means 1 second.
HTML:
<form id="form1" runat="server">
<div>
<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="Label2" runat="server" Font-Bold="True" Font-Names="Microsoft New Tai Lue"
Font-Size="Large" ForeColor="royalBlue" Height="25px" Width="162px"></asp:Label>
</ContentTemplate>
</asp:UpdatePanel>
</div>
</form>
C#:
protected void Timer1_Tick(object sender, EventArgs e)
{
this.Label2.Text = DateTime.Now.ToString("HH:MM:ss");
}
Thank You.