imovie - how to change photo duration

Hi!

I have been reading a lot about the subject here on the support communities, I have tried everything, and nothing works. So here we go:

I am making a slideshow (pictures only) in imovie 10.0.9. I, however, would like to change the duration of all the photos and set them to 6 seconds (for example) each. I have tried to highlight all of them (cmd+a) and then choose Window- Movie properties (or cmd J) - settings-then slide the little slider depending on the duration I am happy with. The thing is, it does not apply to the pictures? I also though that I could adjust the time by clicking the ''enhance'' button and then clicking the time icon, but it's greyed out.

How can I adjust the duration of all the photos? Is there a simple way that will work?

Thank you!