Changing transition time in bulk???

I have 350 slides that need the transition time changed. When I select all to do it in bulk the time adjustment screen goes away. How can I do this without doing them all one at a time?

Make sure you only select slides and no audio, then you can enter a new duration value in the parameters for all slides:

Thank you but I am referring to the TRANSITION duration, not the slide duration. When I select more then one (slide only, no audio) the duration selector disappears.

I am sorry, the same applies here. I no transition is set, you need to unfold the transitions area using the little triangle in the sidebar, then choose a transition and then you are able to set the transition time.