All depends on the type and strength of the Acid. For example if you use concentrated Sulfuric Acid you would not have to worry about the date. Mostly the coin will be gone anyway. However, on the brighter side you will end up with really nice looking Blue Crystals of CuSO4.
Some have tried Vinegar since it contains on an average of 4% Acid. If you have or know someone that has a Lead-Acid battery in thier car, open the hood, open the top of the battery and siphen off some of that for your coins.

All just kidding of course. As already noted that trick that works with Nickels will not work with Copper coins. And in most instances with those Nickels people do more damage than good. Everyone brags about the great finds but never mention how many coins were distroyed in the process.
If your coins are so bad you can not read the date with a 10 to 15X magnifier, forget them.