Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Boo, I can't edit my post above anymore.  I got this additional information after asking how long and placing them on / taking them off.

There isn't really an amount of time for this, if it works, it should happen almost instantly. It could be a good idea to try to make a jig that could pull the horseshoe away from the neodymium magnets at the same time. It probably wouldn't have much effect if they were pulled off separately, but it couldn't hurt...