Can I have a custom desktop wallpaper 'Change Picture' interval?
I found this Apple scripts web page with examples.

There is a line in this script for the change of interval time allowing you to specify it, and you can customize the rest of the script to your needs.

tell application "System Events"
 -- RANDOM ROTATION OF A FOLDER OF IMAGES
 tell current desktop
 set picture rotation to 1 -- (0=off, 1=interval, 2=login, 3=sleep)
 set random order to true
 set pictures folder to file "Mac OS X:Library:Desktop Pictures:Plants:"
 set change interval to 5.0 -- seconds
 end tell
end tell