Before you bring your photos into your Premiere Elements project, go to Edit/Preferences/General and set the Still Image Duration to 1 frame. Then, any photos you add to the program will default to 1 frame in length when you add them to your timeline.
Also note that you'll get best results and the most efficient performance if you resize your photos to 640x480 pixels (72 ppi) before you import them into your project. Using larger photos only slows down and often chokes the program -- without improving the slide's video quality.
Welcome to the forum.
As Steve points out, setting the Edit>Preferences>Still Duration BEFORE Importing, will get what you want.
When doing Stop-Motion, I find that a Duration = 3 to 5 Frames, works best, but that will depend on the images, how far apart, they were shot, and the exact effect that I want. It might take a little experimenting, to get things correct to both your eye, and to the images from the camera.
Also, Scaling the Still Images, prior to Import is a very, very good idea, and especially so, with Stop-Motion, as you will have lots of them.
PS - if you are using Transitions, between the Still Images, you will want to alter the Duration of those too, prior to applying them.