Robert -- I apologize. This is a known bug that was spotted in February and is scheduled for fixing

ACP-1137 - Getting Started - Optimizing Pointing Exposure

Since you are in the trial period you can't see the original conversation. Just move on to Step 8 and start with 30 second pointing image interval. As you become experienced, you may bind you can reduce this and save time. If you are doing long astro-imaging exposures, the difference between 15 and 30 seconds is insignificant for your observatory's overall efficiency.