Unable to spread audio over multiple slides

Hi - thanks in advance for reading. I am using Captivate 2017.

I have a file in which every slide is set to 3 seconds as standard. I want to add prerecorded audio over a number of slides and then adjust the timing to match the audio. I'm clearly doing something wrong but I don't know what.

I go to Slide 4 which has a duration of 3 seconds and a mouse object of 1 second (starting at 2 seconds).

I go to Audio, Import to... Slide and then choose my audio file which is 51 seconds.

I select Distribute the audio file over several slides.

The Slides Audio box appears and I can see the wav file. I turn on Preview.

When I scroll to the right I can see my markers for my other slides. Slide 5 starts after the audio file finishes. I cannot Move Slide 5 marker to the left because it says I have reached the minimum display time for Slide 4.

But Slide 4 originally had a duration of 3 seconds until I added the audio. So I'm at a loss as to how I move the markers to make the audio play over the slides I want.

I hope the above is enough info but please let me know if you need any further info. Thank  you.