class LED_MILLIS{
  private:
    int _pin;
    uint64_t _timer, _time;
    bool _flag;
  public:
    LED_MILLIS(int pin, uint16_t time){
      _pin = pin;
      _time = time;
      pinMode(pin, OUTPUT);
    }
    void start(){
      if(millis() - _timer >= _time){
        _timer = millis();
        _flag = !_flag;
        digitalWrite(_pin, _flag);
      }
    }
};

LED_MILLIS led1 (12,1000);
LED_MILLIS led2 (11,500);
LED_MILLIS led3 (13,250);

void setup() {

}

void loop() {
  led1.start();
  led2.start();
  led3.start();
}