The code which determines Hertz (in proc/sysinfo.c) is
wrong for SMP machines with more than 1 CPU. It comes up
with a value which is the correct value multiplied by the
number of CPUs. The result (perhaps among others) is that
the start time for processes is reported incorrectly in ps.
This bug has apparently already been fixed in the latest
version of procps (procps-990520).
This will also be fixed in the next official release of procps,
2.0.3, which I expect to release soon.