Virtual machines and system time

One observation with virtual machines on my Macbook Pro:

# ntpdate 130.149.17.21
30 Mar 16:58:00 ntpdate[710]: step time server 130.149.17.21 offset 82.381455 sec
# ntpdate 130.149.17.21
30 Mar 16:59:07 ntpdate[711]: step time server 130.149.17.21 offset 33.485510 sec</blockquote>