int latchPin = 5;
int clockPin = 18;
int dataPin = 23;

uint8_t _hours = 0;
uint8_t _secs = 0;
uint8_t _mins = 0;

void setup() {
  Serial.begin(115200); 
  pinMode(clockPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() {
  danceBitch();
  delay(10);
}

uint64_t then = 0;

void danceBitch()
{
  uint64_t now = millis();

  if(now > (then + 1000))
  {
    then = now;

    uint8_t flashLevel = 0;

    if(++_secs > 59)
    {
      _secs = 0;
      flashLevel++;
      if(++_mins > 59)
      {
        _mins = 0;
        flashLevel++;
        if(++_hours > 23)
        {
          _hours = 0;
          flashLevel++;
        }
      }      
    }
    switch(flashLevel) {
      case 3:
        writeTime(31, 63, 63);
        break;
      case 2:
        writeTime(_hours, 63, 63);
        break;
      case 1:
        writeTime(_hours, _mins, 63);
        break;
      default:
        writeTime(_hours, _mins, _secs);
        break;
    }

    if(flashLevel > 0) 
    {
      flashLevel = 0;
      delay(350);
      writeTime(_hours, _mins, _secs);
    }

  }
}

void writeTime(uint8_t hours, uint8_t mins, uint8_t secs)
{
    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, LSBFIRST, secs);
    shiftOut(dataPin, clockPin, LSBFIRST, mins);
    // shiftOut(dataPin, clockPin, LSBFIRST, hours);
    digitalWrite(latchPin, HIGH);
}