elscybe,
This can be accomplished pretty easy. Since you already have your photos on the timeline it is just a matter of "selecting" all of your photos.
One way you can select all of them is by clicking on the first photo on the timeline; then press and hold the "shift" key and click on the last photo. They should all be selected at this time.(make sure you see a blue outline around each photo, which indicates all are selected).
Now you should see the word "duration" on the line right above your photos. Click on it and you should be able to adjust the duration for every photo to any amount of time that you would like. (of course each photo will have the same duration time.)
Also you can preset the duration for a project before placing your photos on the timeline. This can be accomplished by making a change in your preferences.
Look at the top of your window for PD and you should see a little symbol that looks like a gear. Click on that. Look on the left for the "editing" tab. Click on that and once it opens you should see down at the lower part "duration". Set it to what you would like.
Please be advised this is your new default setting for duration and all future duration times will be this unless you change it.
Hope this helps and I am sure if there is a better or easier way to accomplish this someone else will provide you with the information.