I have created a screen recording and add a shape to cover confidential information for 15s during the video. The timing is correct in the Timeline and when I play here it works perfectly but when I preview the slide the shape does not display at all. If I set to 'Show Always' or 'Show Until End' it appears on the preview, but I would only like the shape to show for 15s. I tried publishing to see if this would help, but again, no shape. What am I doing wrong?