#define LED1  2
#define LED2  4
#define LED3  12

unsigned long Time1, dT1;
unsigned long Time2, dT2;
unsigned long Time3, dT3;

void setup() 
{
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(LED3, OUTPUT);
  digitalWrite(LED1, LOW);
  digitalWrite(LED1, LOW);
  digitalWrite(LED3, LOW);
  
  dT1 = 300 / 2;
  dT2 = 520 / 2;
  dT3 = 1000 / 2;    
  Time1 = Time2 = Time3 = millis();
}

void loop() 
{ 
  if(millis() >= Time1)
  { 
    digitalWrite(LED1, !digitalRead(LED1));
    Time1 += dT1;
  }

  if(millis() >= Time2)
  { 
    digitalWrite(LED2, !digitalRead(LED2));
    Time2 += dT2;

  if(millis() >= Time3)
  { 
    digitalWrite(LED3, !digitalRead(LED3));
    Time3 += dT3;
  }
}
}