The wording “use only as directed” is put there for a reason. If you choice to disregard the care instructions then any damage you do to your teeth would be on you.
Maybe before making that choice, you may want to think about getting your teeth whiten by your local dentist. They can not only get your teeth the whitest but they can do it the fastest. It may cost more, but if you are willing to run the risk of damaging your teeth fixing them afterwords will not be cheap either.