how to invisible label after 3second in c#?

if its windows form
you can do it by 2 ways:-

1) use

Thread.Sleep(3000);
label.Visible=false;

2) use a timer
take a global variable of int datatype write in Tiker_Tick() function and set timer's interval "1000"

integervar++;
if(integervar == 3)
{
    label.visible=false;
    timer.Stop();
}

<script type="text/javascript">
    window.onload = function () {
        var seconds = 3;
        setTimeout(function () {
           document.getElementById("<%=lblMessage.ClientID %>").style.display = "none";
        }, seconds * 1000);
    };
</script>

<asp:label runat="server" id="lblMessage" Font-Bold="true"></asp:label>