One method is lock the slide in the Slide Properties and then add audio to match the time they need to stay on that slide and pad with silence or music if needed.
However, there is really no benefit to making them sit on a slide unless it is for purely compliance reasons. Even then, it will only benefit the client and not the learner. If I get to a slide and see it is 5 mins long and locked, I'm going to read it through, then do something else till that time is up, as will most learners. Unless there is some fun game or animation to replay, then I'm all in!