#include "RTClib.h"
#include "time.h"

String startStr = "23:59";
String stopStr = "00:00";

RTC_DS1307 rtc;

bool timerState;
bool oldTimerState = !timerState;

void setup () {
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.begin(115200);
  Serial.println();
  if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
  }

  rtc.adjust(DateTime(2022, 8, 24, 23, 58, 50));
}

void loop () {
  
  DateTime now = rtc.now();
  uint32_t epochTime = now.unixtime();  // epoch time given from internal RTC (seconds since 1970....)
  uint32_t startOfDay = epochTime - (now.hour() * 3600UL) - (now.minute() * 60UL) - now.second();

  uint32_t startTime = startStr.substring(0, 2).toInt() * 3600UL + startStr.substring(3).toInt() * 60UL;
  uint32_t stopTime = stopStr.substring(0, 2).toInt() * 3600UL + stopStr.substring(3).toInt() * 60UL;

  if ((startOfDay + startTime == epochTime) && !timerState) {
    timerState = true;
  }

  if ((startOfDay + stopTime == epochTime) && timerState) {
    timerState = false;
  }

  if (timerState != oldTimerState) {
    oldTimerState = timerState;
    char buffer[25];    
    snprintf(buffer, sizeof(buffer),
            "%02d/%02d/%04d %02d:%02d:%02d  -  ", 
            now.day(), now.month(), now.year(), now.hour(), now.minute(), now.second()
            );
    Serial.print(buffer);

    digitalWrite(LED_BUILTIN, timerState);
    timerState ? Serial.println("Timer ON") : Serial.println("Timer OFF");
  }

  delay(10);
}