How to prolong time of displaying of images in carousel slideshow
Comparing with w3schools example (specifically line &lt;div id="myCarousel"...) - inserting data-interval="30000" there (the line then looks like &lt;div id="myCarousel" class="carousel slide" data-ride="carousel" data-interval="30000"&gt;) does the trick.

In the Jethro theme (and probably in any similar case), this backbone is in the file templates/page.html.twig (in version 2.0 line 85). So that inserting data-interval="30000" there does the trick. The line then looks like &lt;div id="myCarousel" class="carousel slide" data-ride="carousel" data-interval="30000"&gt;. Might be this is not the most elegant way, but it works well.