const int buttonPin = A0;
const int ledPin = LED_BUILTIN;

unsigned long previousMillis;   //obsluha tlačítka
unsigned long previousMillisLED;   //delay LED

const unsigned long interval = 5000;   // 5 seconds  button
const unsigned long RT = 3000;   // delka sviceni led

bool ledOn = false;                    // default, led is off
int lastButtonState = HIGH;            // HIGH is idle (button not pressed)

void setup()
{
  pinMode( buttonPin, INPUT_PULLUP);
  pinMode( ledPin, OUTPUT);
}

void loop()
{
  unsigned long currentMillis = millis();
  unsigned long currentMillisLED = millis();
  
  int buttonState = digitalRead( buttonPin);
  if( buttonState != lastButtonState)  // something changed ?
  {
    if( buttonState == LOW)            // button is pressed ?
    {
      previousMillis = currentMillis;  // remember millis value
    }
    else                               // button is released
    {
      if( currentMillis - previousMillis < interval) // short press 
      {
        digitalWrite( ledPin, HIGH);   // turn led on
        ledOn = true;                  // remember that led is on

        unsigned long currentMillisLED = millis();
        if(currentMillisLED - previousMillisLED >= RT)
        {
        digitalWrite(ledPin,LOW);                             // button is released
        previousMillisLED = currentMillisLED;
        }
        //previousMillisLED = currentMillisLED;
      }
    }

    lastButtonState = buttonState;     // remember new button state






  }
  else if( buttonState == LOW && ledOn) // button still pressed and led is on ?
  {
    if( currentMillis - previousMillis >= interval) // pressed long enough ?
    {
      digitalWrite(ledPin, LOW);
      ledOn = false;
    }
  }
  delay( 30); // a delay as a simple way to debounce the button
}