Using ajax tool kit then work as below code
You got timer:
ASPX
<form id="form2" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<asp:Timer runat="server" id="UpdateTimer" interval="1000" ontick="UpdateTimer_Tick" />
<asp:UpdatePanel runat="server" id="TimedPanel" updatemode="Conditional">
<Triggers>
<asp:AsyncPostBackTrigger controlid="UpdateTimer" eventname="Tick" />
</Triggers>
<ContentTemplate>
<asp:Label runat="server" id="DateStampLabel" />
</ContentTemplate>
</asp:UpdatePanel>

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