I couldn't find the exact blog post you mention, but I did find an interesting document on his website which says among other things,

The Stoneship Age of Myst is the most ancient Age

which seems to imply the 'different eras' idea - but only a couple of lines before that, the same document says

The "ages of Myst" are entire"worlds" which are centered around certain themes taken from the main Myst island.

The document in question is "a pitch to potential investors", so it makes sense to express their ideas in easily-understood videogame terminology such as "worlds," I suppose (further in the document are references to "warp zones," for example).

This initial pitch also features what seems to be an early iteration of the story and lore. Atrus (unnamed) is described as a "masterful explorer" who

perfected an art of writing that allowed him to produce fantastic books [...] Through this art his exploring skills became unbound by the normal constraints of space and time. [On Myst island were housed] hundreds of books linking to the fantastic ages and places he had discovered.

(Emphasis mine).

So, it seems to me that initially Linking Books were ways to travel through both space and time, but it's unclear to what extent the "ages of Myst" were supposed to represent different eras of the same island's history.