Similar question was asked on Serverfault.com. This was the answer.
hwclock man page on RHEL 4.6:
This mode (we'll call it "11 minute mode") is off until something turns it on. The ntp
daemon xntpd is one thing that turns it on. You can turn it off by running
anything, including hwclock --hctosys, that sets the System Time the old fashioned way.
To see if it is on or off, use the command adjtimex --print and look at the value of
"status". If the "64" bit of this number (expressed in binary) equal to 0, 11 minute mode
is on. Otherwise, it is off.
So by the virtue of you running
hwclock --set you have likely turned it off. By the same token you can check the output of the
adjtimex --print to confirm.