I can see that the site is using Owl Carousel and the sliders are initialised in a file named custom.js

According to the docs, I think you want to adjust the navSpeed option.

So initialisation of a slider may look like the following, making sure to adjust the navSpeed as required.

$('.owl-portfolio').owlCarousel({
  items: 4,
  loop: true,
  dots: true,
  nav: true,
  navSpeed: 1000, // ⭐️
  autoplay: true,
  margin: 30,
  responsive: {
    0: {
        items:1
    },
    700: {
        items:2
    },
    1000: {
        items:3
    },
    1600: {
        items:4
    }
  }
})

You can use smartSpeed or autoplaySpeed i hope your problem is solved now in this solution

$('.owl-portfolio').owlCarousel({
  items: 4,
  loop: true,
  dots: true,
  nav: true,
  autoplayTimeout:5000,
  smartSpeed:5000,
  autoplay: true,
  margin: 30,
  responsive: {
   0: {
     items:1
   },
   700: {
     items:2
   },
   1000: {
     items:3
   },
   1600: {
    items:4
  }
 }
})