I had this problem, which is linked to a 50% CPU usage (not very good).
What you have to do is add "no_time_check" in /boot/grub/grub.conf
title Fedora Core (2.6.12-1.1398_FC4)
kernel /vmlinuz-2.6.12-1.1398_FC4 ro root=/dev/vg00/lv00 rhgb quiet no_timer_check
I added the ntpd (network time Protocol) to be sure to be always on the right time at startup.
Everything works fine now, my cpu usage is back to 1% at startup (that is a quick efficient tuning!)