unable to update the date property in AsyncCallback method

Question

unable to update the date property update the the date property

here is my code snippet where im facing issue

public DateTime LastReceivedImplicitMessage { get; set; }

var asyncResult = udpClientReceive.BeginReceive( new AsyncCallback(ReceiveCallbackClass1), s);

private void ReceiveCallbackClass1(IAsyncResult ar) { try {

            UdpClient u = (UdpClient)((UdpState)(ar.AsyncState)).u;
            if (udpClientReceiveClosed)
                return;

            u.BeginReceive(new AsyncCallback(ReceiveCallbackClass1), (UdpState)(ar.AsyncState));
            System.Net.IPEndPoint e = (System.Net.IPEndPoint)((UdpState)(ar.AsyncState)).e;


            Byte[] receiveBytes = u.EndReceive(ar, ref e);

            // EndReceive worked and we have received data and remote endpoint

            if (receiveBytes.Length > 20)
            {
                //Get the connection ID
                uint connectionID = (uint)(receiveBytes[6] | receiveBytes[7] << 8 | receiveBytes[8] << 16 | receiveBytes[9] << 24);


                if (connectionID == connectionID_T_O)
                {

                    ushort headerOffset = 0;
                    if (T_O_RealTimeFormat == RealTimeFormat.Header32Bit)
                        headerOffset = 4;
                    if (T_O_RealTimeFormat == RealTimeFormat.Heartbeat)
                        headerOffset = 0;
                    for (int i = 0; i < receiveBytes.Length - 20 - headerOffset; i++)
                    {
                        T_O_IOData[i] = receiveBytes[20 + i + headerOffset];
                    }
                    
                    //Console.WriteLine(T_O_IOData[0]);


                }
            }
            
            LastReceivedImplicitMessage = DateTime.Now;

        }
        catch (Exception ex) { }
    }

"LastReceivedImplicitMessage" is not getting updated with datetime.now