Defining what time is in a black hole is nothing like Classical Mechanics. Mathematical models indicate no empirical data, rather just the best consensus among scientists, which of course is a speculation among such theories of time. You'll find that many of these theories are constantly being disregarded as more knowledge of the topic increases. This is a good indicator that one must be skeptical at all times; because when these theories are standing solely upon the scientists' opinions, and not graspable data (therefore pseudoscience), our "knowledge" is comparable to retrospectively looking at the middle ages...
Also, I did not criticize the use of time for practical applications whatsoever. We need a way to track time so we can schedule our daily tasks, or, in your example, keep track of time in relation to velocity and position around the earth. I do, however, believe science theories involving time do not agree with theology as a whole.
One example is:
Not enough hours in the day? Scientists predict time will stop completely - Telegraph.
Our life, universe, or presence of time cannot end by scientific means because that is not what the Bible teaches (Tribulations, New Jerusalem etc...). I'm just saying, you can't accept some of these abstract theories and still fully be invested in the Christian belief.