I think I should go from another direction.
Yes, obviously the Hubble constant refers to intergalactic motion, and cannot be properly applied to intragalactic effects. That does not necessarily mean that such effects do not exist (it just means that they are too minor to measure, and/or usually overshadowed by other effects; that said, I believe that GPS is precise enough that Hubble drift would've affected it if it worked on these scales, but I hadn't done the calculation, and for all I know perhaps it does and it's just brushed off as another easy correction).
But that aside, consider what the Hubble constant means: it is (roughly, due to complicated inflationary models, but it works as a first approximation) the inverse of the time since Big Bang. Everyone knows how much it had been since Big Bang: 13 billion years (give or take a bit).
That means that the fraction of the Hubble expansion that had occurred over the last X million years is about X/13000. (Well, more like 13600 really, but whatever.)
For x=70 (an appropriate value for seeing T-Rex - 60 would put the traveller in the early Paleogene*), this would be 70/13000, or about 1/200. Yes, Sam Blitz's estimation is correct: about half a percent, or, for typical human height, about a centimeter.
If they wanted to visit the Triassic period instead, the time gap would roughly triple, so they would instead be about three centimeters taller. Still not significant (and probably not noticeable).
*) Which might be the reason he's seeing chickens instead of dinosaurs: because all the big dinosaurs have gone extinct, and the few that still remain (mainly ancestors of modern birds) are tiny and look like chickens! Since they also happen to be fairly close relatives of T-Rex (and even closer, IIRC, of Velociraptor), the result is a lot similar to a chicken-sized T-Rex (except with feathers, obviously - though perhaps the actual T-Rex also had them).