The key point in GR is that time is local. Clocks slow down in a gravitational field. Since the Earth's gravity is stronger than Mercury's, it will take longer (seen from a distance) for the same process to occur on the Earth's surface than it will on Mercury's. The rate change is infinitesimal unless the gravitational field is very, VERY intense.

A practical experiment is to compare an atomic clock on the Earth's surface to one in orbit. Read about it here:

[link|http://www.phys.virginia.edu/classes/252/general_relativity.html|http://www.phys.vir...ativity.html]

BTW, general relativity is incomplete in a sense since mass is just as much a mystery in it as it is in Newtonian gravity. However in my work mass becomes an aspect of geometry connected with curvature in the 5th and 6th dimensions, so this gets closer to the truth. The jury is out.