So, now that we can rotate our wallpapers, why not give a timer to control the difference in the rate of change?

As it sits now you can only change them starting from the same time. I have my timer set to one, so every minute they both change. That's nice but what if I want change every thirty seconds? See what I am getting at? One changes at :00, the next at :30 the first at 1:00 etc.
I imagined a slider that comes up when both desktops are set to timer, sitting above the minutes to change. Done by percentage, seeing as how you have many different values for what it would actually be offsetting. Right in the middle, above the slider would be the mid point, in this instance :30

Another little thing that shouldn't be too hard would be a tick box for the option to make it so both monitors will not have the same image on them at the same time, as well as another tick box for disallowing both screens to have images from the same folder. -- forces the first tick to be greyed out.
One last thing for now: Disallowing either monitor to have pictures from the same folder consecutively.

Food for thought.

I agree! Good point!

Yea you have the gist of it right, execution will be a pain though.. My idea seems the only workable approach. Also, did you use a tick box for the allowance of copy images? I wouldn't think so from the changelog.....