A person from the year 2250 goes back in time. They go back 60 Million years, because they want to observe dinosaurs. Imagine their surprise when they see T-Rex's running around like little chickens!!
That's because they neglected the Hubble Expansion that had occurred in the last 60 Million years. So they are much larger than anything that existed so far in the past.
Is this correct?
No, because Hubble expansion has negligible effects on very small systems (such as human beings).
Here is an answer which explains the maths behind it : Can the Hubble constant be measured locally??
Shortly, no, this is not correct.
Here's why. Hubble's law gives us that for a distance of one megaparsec, that space expands by approximately 70 km/s (the data varies, but it's somewhere between 60-80 km/s - it doesn't matter, and you'll see why). Now, how tall is your average human? Let's be generous and say your time traveler is 2m tall. Now, how many MPc is that? Oh, about $6.4 \times 10^{-23} \text{ MPc}$. So, even naively neglecting the fact that the expansion of the universe does not affect gravitationally, electromagnetically, chemically, or otherwise bound bodies (see mlg's answer above, i.e. the earth does not expand with the universe), if we assumed it did, then we would find that your 2m tall person has grown about a centimeter. Not dwarfing anything!
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).
