The behaviour you have described is perfectly normal.
This is configured in your XP mode .vmc file
...
<host_time_sync>
<enabled type="boolean">true</enabled>
<frequency type="integer">15</frequency>
<threshold type="integer">10</threshold>
</host_time_sync>
...
To disable time sync change enabled to false.
Before you must shut down XP Mode.
...
<host_time_sync>
<enabled type="boolean">false</enabled>
<frequency type="integer">15</frequency>
<threshold type="integer">10</threshold>
</host_time_sync>
...
Then restart XP mode.