ASP.NET Ajax ConfirmButtonExtender doens't work

Question

Here is my problem in 3 steps:

1 - ConfirmButtonExtender btn0 is pressed

2 - Popup open, inside it there are 2 buttons (Confirm and Cancel)

3 - Confirm button is pressed AND THEN btn0_Click is called

I WANT THIS TO BE CALLED WHEN btn0 IS PRESSED THE FIRST TIME

.aspx

<asp:Button runat="server" ID="btn0" Text="OK" OnClick="btn0_Click" />    

<cc1:ConfirmButtonExtender ID="ConfirmButtonExtender_GetHour"
runat="server" TargetControlID="btn0" OnClientCancel=""
DisplayModalPopupID="ModalPopupExtender_GetHour"
ConfirmOnFormSubmit="true" 
ConfirmText="yo?" />

<br /> 

<cc1:ModalPopupExtender ID="ModalPopupExtender_GetHour"
runat="server" PopupControlID="PNL_getHour"
TargetControlID="btn0" OkControlID="ButtonOk_GetHour"
CancelControlID="ButtonCancel_GetHour"
Enabled="True"> </cc1:ModalPopupExtender>


<asp:Panel ID="PNL_getHour" runat="server">
   POPUP WITH A BUTTON AND A CANCELBUTTON
</asp:Panel>

.cs

protected void btn0_Click(object sender, EventArgs e)
{
     //I WANT THIS METHOD TO WORK WHEN BTN0 IS PRESSED 
     //AND NOT WHEN THE POPUP'S CONFIRM BUTTON IS PRESSED
}