Can't change slide duration

Hi guys,

I need my slides to end just after the last animation so I'm using the Audio Editor to adjust the duration. For slide 1 the situation initially looks like this:

I change it to this and click Save & Close:

When I preview the slide, it has absolutely no effect on slide duration. When I open the Audio Editor again, it goes back to the one pictured in the first screen shot. What am I doing wrong??

Thanks,

Arek