how to retain a button clicks action with a sleep against another button click action without sleep

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C#

ASP

Hi..,
My problem is i have two labels and two buttons in two different update panel in asp.net.
The update panels contains two buttons.
when buttons are clicked.., it will update the corresponding label text.
The issue is, suppose i gave a delay of 5 seconds in my button1_click() method, when i click button1 and button2 immediately, label2 is gettin updated.., whereas label1 is not getting updated.

can u suggest me wher im goin wrong??

this is back-end code-

protected void Button1_Click2(object sender, EventArgs e)
        {
            System.Threading.Thread.Sleep(5000);
            Label1.Text = "Hello";
        }
        protected void Button2_Click1(object sender, EventArgs e)
        {
            Label2.Text = "World";
        }