Millis

int led1 = LOW;

int led2=LOW;

unsigned long lastTime_A = 0;

unsigned long lastTime_B = 0;

int interval_A = 1000;

int interval_B = 500;

void setup() {

 pinMode (13, OUTPUT);

 pinMode (12, OUTPUT);

}

void loop() {

 unsigned long currentTime = millis();

 if (currentTime - lastTime_A >= interval_A) {

lastTime_A = currentTime;

 if(led1 == HIGH){

  digitalWrite(13, LOW);

  led1 = LOW;

 } else{

  digitalWrite(13, HIGH);

  led1 = HIGH;

 }

 }

 if (currentTime - lastTime_B>= interval_B) {

lastTime_B = currentTime;

 if(led2 == HIGH){

  digitalWrite(12, LOW);

  led2 = LOW;

 } else{

  digitalWrite(12, HIGH);

  led2 = HIGH;

 }

 }

 }