Locking/checking out

You can use cookies if you don't want to store any data in database
Here's just a sample code to enable and disable a textbox, you can modify it to lock your schedule. Though this won't reside anywhere within the application but be a client side setting.

protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.Cookies["State"].Value == "Locked")
        {
            TextBox1.Enabled = false;
        }
        else if (Request.Cookies["State"].Value == "Unlock")
        {
            TextBox1.Enabled = true;
        }

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        TextBox1.Enabled = false;
        Response.Cookies["State"].Value = "Locked";
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        TextBox1.Enabled = true;
        Response.Cookies["State"].Value = "Unlock";
    }

Hope this helps