Set Interval for Slideshow

I am using this JS code I found to make a slideshow work:

Code:

---

<script>
    var slideIndex = 1;
    showDivs(slideIndex);
   
    function plusDivs(n) {
      showDivs(slideIndex += n);
    }

    function showDivs(n) {
      var i;
      var x = document.getElementsByClassName("hp-slides");
      if (n > x.length) {slideIndex = 1}
      if (n < 1) {slideIndex = x.length}
      for (i = 0; i < x.length; i++) {
        x[i].style.display = "none"; 
      }
      x[slideIndex-1].style.display = "block"; 
    }
    </script>

---

But the images move right as I click = too fast/ not elegant.

I saw this other code in other JS slider examples, which made the slides move slower (Those other codes didn't work for me for other reasons (couldn't be resized, needed complicated/hidden jQuery, etc.))

Code:

---

    setInterval(function() {
    showDivs()
    }, 5000);

---

Is there a place to put it in that would make the slides go slower (5s in this case)? I changed the name to be one of the function names (showDivs), but that made no difference.

I'm already on 3-4 days looking for a simple slider with arrows that will scale with the page and losing my mind.
Thank you!