int relay = 13;
unsigned long onTime = 10000, offTime = 5000, lastTime = 0;
bool led = false;

void setup() {
  pinMode(relay, OUTPUT);
  Serial.begin(9600);
  Serial.println("ON=10 and OFF=5");
}

void loop() {
  if (Serial.available()) {
    String cmd = Serial.readStringUntil('\n');
    cmd.trim();
    if (cmd.startsWith("ON=")) onTime = cmd.substring(3).toInt();
    if (cmd.startsWith("OFF=")) offTime = cmd.substring(4).toInt();
  }

  unsigned long now = millis();
  if (led && now - lastTime >= onTime) {
    digitalWrite(relay, LOW);
    led = false;
    lastTime = now;
    Serial.println("RELAY OFF");
  } 
  else if (!led && now - lastTime >= offTime) {
    digitalWrite(relay, HIGH);
    led = true;
    lastTime = now;
    Serial.println("RELAY ON");
  }
}