delaywithoutdelay

bool firstProc = true;
unsigned long previousMillisFp = 0;
const long intervalFp = 5000;
int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  if (firstProc == true)
  {
    check();
  }

}

void check()
{
  digitalWrite(ledPin, HIGH);
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillisFp >= intervalFp) {
    previousMillisFp = currentMillis;
    Serial.println("5 seconds elapsed");
    digitalWrite(ledPin, LOW);
    firstProc = false;

  }
}