FS now tries to determine how accurate the timing is by doing some tests with 1ms sleeps.
Most 64 bit CentOS box I have seen can easily calibrate.
If you are having that error alot but the calls still sound ok, it's safe to ignore it.
you can also start FS with -nocal to skip this test.
Also make sure you do not have any other cpu-intensive application on your box possibly competing for resources.