Delay/Sleep for 8 hours?

Projects Programming
5 
unsigned long SleepStart = 0;
const unsigned long SleepInterval = 32400000UL;
void loop() {  

 switch (mode) {
    case NORMAL:
      analogWrite(ULNOutputPin, 255);
      break;
    
    case SLEEP:
      analogWrite(ULNOutputPin,0);
      if (millis() - SleepStart > SleepInterval)
          mode = NORMAL;  // Resume normal operation
     
      #ifdef DEBUG
          Serial.print("\nSleeping...");
      #endif
      break;
  }


  // Button "Sleep" pressed?
  if (sleepButton.pressed()) {

    if(mode == NORMAL) {
      mode = SLEEP;
      SleepStart = millis();
    } else {
      mode = NORMAL;
    }
    
    #ifdef DEBUG
      Serial.print("\nSleep-Button pressed, mode is now ");
      Serial.print(mode);
    #endif   
  }

}