The Cosmic Treadmill, while it never came up in the JLU, was in the Toonverse, in
Justice League Adventures #11,
The Moment.
The Atom creates it so that Wally can return Abra Kadabra to the future. Kadabra, for those of you who aren't up on the Flash rogue's gallery, was from the future, using it's technology to act as a magician in the present. Anyway, while they're on their way back, they pass themselves, and it turns out David Clinton, better known as Chronos, is manipulating the Time Stream to save his brother, a fireman, from dying in the line of duty.
And it's making everything fall apart. So in the end, Atom and Flash have to find a way to stop Chronos and let Bobby Clinton die.
In other news, I've decided that Wally was the tender age of 17 when he first joined the Justice League. I've always seen his purported idiocy in the first seasons to be a little harsh; he's not stupid, he's young. So as of my story? Mid-twenties. And Bruce is mid-thirties. Does that make Diniverse continuity wonky? Maybe. When is Justice League continuity
not wonky?
( Ten scans of that. )