With muratic acid you need to add some good peroxide to the acid it speeds it up. And submerge the board and watch the exposed copper vanish .
A good variation of that is to use an aquarium bubbler instead of hydrogen peroxide, but it takes a day or two to prepare for the first time. But once you have it, it lasts forever. When the mixture becomes dark from use, just bubble more air through it until it becomes transparent green again. This way, the water in the peroxide is not diluting the solution down and you can repeatedly reuse it (it gets stronger and stronger instead of more watered down). I have been using the same captain morgan bottle of it for 7 years and have yet to add more muriatic acid to it, just air. Eventually, it may need more acid, but it takes a very long time. Just don't use an aquarium stone. As tempting as it is, they dissolve in the acid, lol. Just use a rubber hose and a cotton ball to keep it from splashing out from bubbling action. To however much muriatic you initially use, add enough copper to consume about half of it and bubble air through it until the copper is gone and the solution is transparent green. You don't want to add so much copper initially that the copper chloride precipitates out leaving no muriatic for reactivating later..
A quick diy etchant is vinegar, 3% hydrogen peroxide and table salt. It's just a little slower. The salt reacts with the vinegar to produce hydrochloric acid in situ (weaker version of muriatic). I never get tired of the copper surface exploding with bubbles when the salt settles on the copper.
Copper chloride is mildly toxic to humans and extremely toxic to aquatic life. If you decide you want to destroy it, just add aluminum foil. It will precipitate out the copper. Using my method above, you should never need to do that unless you make lots of it. The vinegar method also produces copper chloride, and it should be treated the same way, but I'm not the EPA lol. I do it because I don't want it in our well water, but most people simply flush it.