How do I change the slide length in Storyline

I am having the opposite problem. Granted I am a newbie. But I don't want to slide to advance regardless of timeline unless the user clicks my custom Next button. I have the button on the slide, but if I stop in the middle of previewing my slide (like to talk to my DH about something I did on the slide), then as soon as it reaches the end of the timeline, it just advances on its own, even though I never clicked next. What am *I* doing wrong? It seems dumb to just randomly drag the timeline to be really long just so that the person who gets interrupted in the middle of using my module doesn't have it automatically advance. I am sure there is a simple fix; I can't find it. THanks.