It is run as part of the daily cronjobs. The hourly, daily, weekly and monthly jobs are started by run-parts from /etc/crontab. However, the time listed in /etc/crontab only indicates when the first daily cronjob is started. The start time of an individual daily cronjob depends on the running time of the other daily cronjobs, as they are run one after another.
If you really need to know an exact start and stop time of this particular cronjob, you could modify the cronjob to write a timestamp to some file or send an e-mail for instance, but Plesk might overwrite these changes upon Plesk upgrades.