When using muriatic acid and hydrogen peroxide, the etching time mostly depends on the concentration of hydrogen peroxide used. I usually get 12% peroxide from a beauty supply store. With this concentration mixed 2 to one with muriatic acid the etch time is around 2 to 3 minutes. This is a very exothermic reaction, and the solution will get hot very fast.. You really have t o watch closly with this concentration, because it can over etch very quickly. I usually dilute this down to 6% to get around a 6 minute etch time. With the 3% from a drugstore I usually have a 12 to 15 minute etch time. Peroxide can decrease in concentration after it ages or exposed to air. in a nearly empty container. DuWayne KV4QB