System.Timers.Timer timer = new System.Timers.Timer();

timer.Interval = 1;  //одна миллисекунда
timer.Elapsed += OnTimedEvent;
timer.Enabled = true;

private void OnTimedEvent(Object source, System.Timers.ElapsedEventArgs e)
{
     msecs++;
}

while (connected)
{
    if (msecs >= timestamp)
    {
         timestamp = msecs + 1000;  //16 sec
    }
}

 private void SendCanFrames()
 {
       if (tx_can_msg.Length == 0) return;

       VSCAN_MSG[] l_msgs = new VSCAN_MSG[2];

       while (running)
       {
            for (int i = 0; i < tx_can_msg.Length; i++)
            {
                if (tx_msec_cnt >= can_messages[i].TimeStamp)
                {
                     l_msgs[0] = tx_can_msg[i];

                     // send CAN frame
                     CanDevice.Write(l_msgs, 1, ref written_cnt);

                     can_messages[i].TimeStamp = tx_msec_cnt + can_messages[i].Period;
                    
                     this.Invoke(
                      (MethodInvoker)delegate
                       {
                              can_messages[i].CountRun++;
                              dataGridViewCanTx.Rows[i].Cells[4].Value = can_messages[i].CountRun.ToString();
                       });   
                       
                    }
                }
            }         
        }

TimeSpan interval;
DateTime dt1 = new DateTime();
DateTime dt2 = new DateTime();

while (connected == true)
{
    dt1 = DateTime.Now;
    interval = (dt1 - dt2)

    if (interval.TotalMilliseconds >= 20)
    {
          dt2 = DateTime.Now;
     }
}