millis

// Globals
unsigned long previousMillis = 0;
const long interval = 5000;

  // Blocking "like delay()"
  unsigned long start = millis();
  while (millis() - start < interval) {
    // ...
  }

  // Non-blocking
  if (millis() - previousMillis > interval) {
    previousMillis = millis();
    // ...
  }