unsigned long previousMillis;
unsigned long interval;
bool enable;
int ledState;

void setup() 
{
  pinMode( LED_BUILTIN,OUTPUT);
  
  // start millis timer
  interval = 2000UL;
  ledState = LOW;
  enable = true;
}

void loop() 
{
  unsigned long currentMillis = millis();

  if( enable)
  {
    if( currentMillis - previousMillis >= interval)
    {
      previousMillis = currentMillis;

      if( ledState == LOW)
      {
        ledState = HIGH;   // set new led state
        interval = 8000UL; // set new interval
      }
      else
      {
        ledState = LOW;    // set new led state
        enable = false;    // stop own millis-timer
      }
      digitalWrite( LED_BUILTIN, ledState);
    }
  }
}