Check the hide box to ensure if it is checked or not.

Please insert a screenshot of the Timeline panel. You probably have one or more interactive objects (buttons or Text Entry boxes) which do pause the Timeline before reaching 20secs.

Check also the On Enter action of the slide. Is it perhaps set to Pause, which is the case in multiple slide of the included Quick Start Projects.

To learn more about pauses and pausing points, and how this affects items on a slide have a look at:

http://blog.lilybiri.com/pausing-captivates-timeline

One example why you may be confused: if you have narration (slide audio) on the slide, the audio will not be paused automatically by a pausing point, but needs to be done by an option in the Properties panel of the interactive object. The playhead will pause, the objects after the pausing point will not appear (like your Next button) but the audio will continue to play, animations (OAM or GIF) will continue to play as well.

1. Take a close look at the timeline – is there something else on the slide with a pausing point prior to the button?
2. Do you accidentally have it set as hidden on publish? (Eye icon next to name)