I recently described time as a phenomenon "on the inside of objects." Peter Gratton objects that time is "at the surface level of objects" for Harman, because the latter describes it as the tension between sensual objects and sensual qualities. Gratton argues, "if time is at the surface of where things relate then it is not within the object."
Short answer: we're both right.
Longer answer: it's necessary to recall that for Harman, sensual objects only exist in experience (or "confrontation," if you prefer that lingo). And experience only exists within some specific experiencing entity—not as an abstraction in the world. Sensual objects are the only entities that come into direct contact with real objects ("sincerity," Harman calls it) because they have to be; the sensual "is never something truly autonomous" (The Quadruple Object, 126), but exists in relation to real objects. In Harman's case, the relation between one object and another, mediated through the sensual object, itself produces another (real) object, which is the relation! Time can only exist on the inside of this real object.
Here's the key passage in QO (116):
The mind cannot serve as both part and whole simultaneously. Instead, both the mind and its object are encompassed by something larger: namely, both exist inside the object formed by the relation between me and the real tree, which may be rather different from the trees found in everyday life.
As Harman argues on the page that follows, any relation immediately generates a new object: "insofar as we somehow connect with a real object outside us, giving rise to perceptions of sensual trees, mailboxes, or blackbirds, we have somehow liked with that object to form a new real object." Time may be a tension between sensual qualities and sensual objects, but the sensual object can only be birthed within the encounter of confrontation in the first place.
Harman's fourfold account of objects might be best understood as an account of object texture rather than object discreteness; Graham called it a "bumpy ontology" in Zagreb recently. The items in the fourfold are not on an even playing field with one another, rather, they describe a kind of infinitely recursive structure in which sensual objects are always jutting out from real ones.