Iets als dit regelt de NTP update in de aquacontrol software:

//    wait a specific interval, accounting for rollover with subtraction!
  
unsigned long timerInterval = 50;  // this is the interval in milliseconds
unsigned long nextTimer = millis() + timerInterval;
  
void loop() {
  lastMillis = millis();
  if ( ( long ) ( millis() - nextTimer ) >= 0 ) {
    Serial.println( "Interval has passed." );    
    nextTimer += timerInterval;
    //do some more stuff...
  }

//rest of the main loop
}

Alles nur geklaut:
http://playground.arduino.cc/Code/TimingRollover