Yeah, I'll have to think a lot harder about full PoS to maybe answer that question. One thing to note us that there are certain hidden timing assumptions (eg in casper-ffg, there is the 4 month unbonding period, and the timescale over which an inactivity leak occurs) that are necessary for security (they seem to correspond to the time scales needed for weak subjectivity social consensus and hard forks respectively)
I think the most precise name might be something like "affine timestamp"; you don't actually need timestamp wrt the big bang but being able to measure the rate-of-time is stronger than merely being able to order events
