class Timer {
  float time;
  int starttime, lasttime;
  Timer(float t) {
    time = t;
    starttime = second();
    lasttime = starttime;
  }
  void update() {
    if (millis() - starttime >= lasttime + time) {
      lasttime = millis();
      //runs once every time "time" (millis as float) passed:
      nextSlide(autoplayMode);
    }
  }
}