I read that the viewpoint of nihilism denies the existence of objective values and meaning. But does it also say that the values never existed, never can or will exist or just that these values don't exist now?
Both are possible. Nihilism could just mean the current values are without meaning. But usually, for example, in Nietzsche, 'objective values' cannot exist, because values are subjective perspectives.
Nihilism is the philosophy of the "nothing" or more the "emptiness"
Nihilism do not say they are no values ( because by saying that its already a" value" ) it says that all those values come from Nothing.
It means that the values are built on nothing more than you own self and not on something hidden.
And if you are a part of the world inside it, and plus a simple "mortal" with no escape from your self those values can just be built on subjectivity because you cannot be everything you want or not be, so your values are human and made up from scratch.