Timers in Arduino

Projects General Guidance
3

Indeed, use millis(), that's the easiest. You get something like this:

unsigned long startTime;

void setup() {
  startTime = millis();
}

void loop() {
  if (millis() - startTime > 2 * 60 * 60 * 1000) {
    startTime = millis();
    doTwoHourThing();
  }
}