add date to database if checkbox checked in gridview

I have an Ordering system showing Orders that have been received and also orders that are outstanding. If the Order is received and the checkbox is then checked I would like to add the date to the database when the order was received. Obviously I would only like to add the date to the row that has been checked. Thanks in advance.

relevant HTML as follows:

                            <asp:GridView ID="gvOpenOrders" runat="server" AutoGenerateColumns="False" Width="100%" CellPadding="4" ForeColor="#333333"
                                GridLines="None" DataKeyNames="PurchaseOrderID" AllowPaging="True" AllowSorting="True"
                                OnSorting="gvOpenOrders_Sorting" EnableViewState="true" OnPageIndexChanging="OnPageIndexChanging" PageSize="15" ViewStateMode="Enabled">
                                <AlternatingRowStyle BackColor="White" />
                                <Columns>
                                    <asp:TemplateField HeaderText="Is Received" SortExpression="IsReceived">
                                        <ItemTemplate>
                                            <asp:CheckBox ID="chkRcvd" runat="server" AutoPostBack="true" Checked='<%# Bind("IsReceived") %>' Enabled='<%# Eval("IsReceived") = False %>' OnCheckedChanged="chkRcvd_CheckedChanged" />
                                        </ItemTemplate>
                                    </asp:TemplateField>

I am currently updating the database when a Update Received button is clicked, see below:

Protected Sub btnUpdateReceived_Click(sender As Object, e As EventArgs) Handles btnUpdateReceived.Click

    con.Open()
    For Each row As GridViewRow In gvOpenOrders.Rows
        Dim purchaseOrderID As Integer = Convert.ToInt32(gvOpenOrders.DataKeys(row.RowIndex).Values(0))
        Dim isReceived As Boolean = TryCast(row.FindControl("chkRcvd"), CheckBox).Checked

        cmd.CommandText = "usp_UpdatePurchaseOrder"
        cmd.CommandType = CommandType.StoredProcedure
        cmd.Parameters.Clear()
        cmd.Parameters.AddWithValue("@OrderID", purchaseOrderID)
        cmd.Parameters.AddWithValue("@IsReceived", isReceived)
        cmd.ExecuteNonQuery()
    Next
    con.Close()
    Response.Redirect(Request.Url.AbsoluteUri)

End Sub

I know that there is a checkbox_CheckedChanged event but I am unsure how to use it.