Modal popup extender ?

Hi guys I'm using modal popup extender for dispalying a window while loading something. I want to show modal pop up on button click, but it should get hide after loading. Here I've used threading mechanism to create artificial delay for 8 secs. But how can I hide modal pop automatically after 8 secs. Here's the code that I'm using..

<asp:Button ID="btnname" runat="server" onclick="btnname_Click" Text="Click" />
<asp:ModalPopupExtender ID="ModalPopup" runat="server"
DynamicServicePath="" Enabled="True" TargetControlID="btnname" BackgroundCssClass="modalBackground"
CancelControlID="btnClose" PopupControlID="pnldis">
</asp:ModalPopupExtender>
<asp:Panel ID="pnldis" runat="server" CssClass="modalPopup" align="center" style = "display:none">
Loading ...<br />
<asp:Button ID="btnClose" runat="server" Text="Close" />
</asp:Panel>

protected void btnname_Click(object sender, EventArgs e)
{
System.Threading.Thread.Sleep(8000);
lblmsg.Text = "Hi " + txtname.Text;
ModalPopup.Hide();
}

.modalBackground
{
background-color: Black;
filter: alpha(opacity=90);
opacity: 0.8;
}
.modalPopup
{
background-color: #FFFFFF;
border-width: 3px;
border-style: solid;
border-color: black;
padding-top: 10px;
padding-left: 10px;
width: 300px;
height: 140px;
}