Philip, there are some very obvious problems with some points on that site you linked to.
Take this point (which you implied refered to caesium clocks and E=mc2, though I don't see the connection) for example
quote:
11 . Some who believe in an old universe have a different explanation. Those isotopes are extinct because so much time has passed. However, this explanation raises a counterbalancing question: How did those isotopes, and 97% of all elements, form? The standard answer is that these elements appeared during supernova explosions. This is actually speculation, because essentially no supporting evidence has been found. Besides, all supernova remnants we see in our galaxy appear to be less than 10,000 years old. This is based on the well-established decay pattern of a supernova’s light intensity in the radio-wave frequency range.
The problem here is two fold;
1) that the overwhelming majority of supernovae occured early in the life of the galaxy when it was dominated by massive stars (we know that from studies of very distant galaxies), and so the contribution of modern supernovae to the abundances of heavy elements is minor.
2) by their very nature supernovae remnants disperse with time, and so the absence of really old remnants is hardly surprising. And the 10000 year age is wrong too - "Tycho's Star" in Cassiopeia exploded at least 20000 years ago, and SN1987A in the LMC about 169000 years ago.
Alan