What computer operating system for your Premiere Elements 13? Have you updated 13 to 13.1 yet using an opened project's Help Menu/Updates.
To your immediate question...
You can set the still image duration for your photos in two ways....
A. Set up before Import....See Edit Menu/Preferences/General and option for Still Image Default duration. There the units are in frames (150). In a 30 frames per second system (NTSC), that 150 frames = 5 seconds. You can adjust that setting. If you need help with that I will give more details.
The above works for only those stills imported after the setting has been made in preferences. And, you need to reset it for new work. It does not automatically reset to 150 frames.
B. After the still is imported and on the Expert workspace Timeline, right click it, select Time Stretch, and then, in the Time Stretch dialog set the duration accordingly. There the representation is in a timecode format (hours;minutes;seconds;frames). So, for 5 seconds, that would read 00;00;05;00. You can do one at a time or more than one at a time. More details if needed.
Please consider and give more details.