Spews (Simple Process Excluding Wallpaper Switcher) allows for auto-switching your wallpapers on a user-defined schedule.
To use Spews, add your image folders, choose wallpaper options and then click the enable button at the bottom. You have the option to check/uncheck the image paths as needed. Keep in mind, only checked paths will be scanned for images.
Spews additionally includes a feature that can automatically suspend the wallpaper switching if it detects any process names configured in the exclusions section. This can be useful when running games whose graphics corrupt if the wallpaper is changed for instance.