If you want to set intervals of your choice, you can do it by modifying the registry. Please follow the below steps to set the slideshow intervals:
Open Run and type regedit.exe
HKEY_CURRENT_USER\Control Panel\Personalization\Desktop Slideshow
In here, the two important values are the Interval, and Shuffle.
Double click on Shuffle, and change the value to 1. OK.
Then change the Interval by double clicking on it. You'll first want to change the Base to Decimal, rather than Hexadecimal (otherwise you'll get unexpected interval values). Then change the value to your desired time, in milliseconds (10000ms for 10 seconds).
You can exit regedit now. The final step is to restart Explorer. You can do this through Task Manager if you know how, otherwise simply restart your computer.