Display layers against timeline triggers

I have a project where I have a slide with a base layer that contains video and audio (approx. 1m 30 secs in length) and 12 layers; on the click of a custom button, layer 1 is displayed with a caption stating the video action and the audio content, set to the correct timeline duration. What should happen (according to my triggers), when the timeline ends on layer 1, layer 2 is displayed and so on, this is not happening... layer 1 is displaying for far longer than the timeline specified. While all the layers are eventually displayed, they are not adhering to the prescribed timelines, meaning that the content of the remaining 11 layers is displayed long after the video and audio have completed.

I have another slide in the same project, with audio but no video and is working like a dream!

Any tips to resolve would be gratefully received!