Concerning calls to gettimeofday():
I wrote the obvious C program to spin around in a loop just calling
gettimeofday().
On a 250MHz Ultra I running Solaris 2.8,
the cost of a call to gettimeofday() was 1.6 usec.

To take 1% of the CPU, you'd need to make 6,250 calls per second.
(More on faster machines.)