I have done this. Example: you have 26 pictures, but on first screen can only load 20. Solution, ONLY load ONE on the fist screen, adjust the time, say 5 seconds. Click save at top. Go to schedule screen.
Sometimes we you see your loaded picture it's time changes to 10 mins. CHANGE it back to 5 or 10 seconds, on the bottom you will see "Open Content Browser".
Click the open content browser.
Have a folder in your documents folder on your computer label display file, if you open that file it will load on the bottom all files in the "display" folder. There you can click and drag them up to the play list. BY DEFAULT, it enters 5 seconds for each but you can adjust each one. Save then install as normal.
I have 45 slides on one location