This can take anywhere from several days to several months, depending on how crusty your find is. Another method I've seen is by building a home-made electrolysis machine. One clip is attached to the object to be cleaned, the other to a stainless steel spoon or large bolt and dumped into a glass container containing a salt water or baking soda and water solution. The adapter is then plugged into the wall. Cleaning time varies depending on the mA rating of the adapter.
Electrolysis is ideal for anything metallic, including iron objects.
I don't recommend it, tho, because the adapter tends to heat up quickly, and you can't leave it unattended for a single minute because of the very real danger of the adapter starting on fire. Especially when it involves using electrical accessories in ways that weren't originally intended. It seemed to me that asking the ANA the best way to clean coins would be like asking paleontologists at Chicago's Field Museum the best way to dig up dinosaur bones. According to ANA Museum curator Robert W. Hoge, there is no best way. The closest thing to a coin conservator in my area is Maury The Fist, and he's a bigger authority on burying things, not digging them up.