It's still not really "correct" IMO, I think it needs to be "UnitIntervalValue" as someone said above. I'd expect that things of type "UnitInterval" would be intervals, not values. "UnitInterval" would be like calling the type "Int32Range" instead of "Int32".

(NB: "In real life" I would never "correct" someone for calling it "UnitInterval", it's good enough -- but given this is a pure discussion of semantics...)