In previous versions of the product, the daily password checks were configured to start at a specific time of day. At this time, it would load the test queue and then proceed with checking every account in this queue until it was done.
With the introduction of Check Profiles in 2.5.915, it is now possible to assign profiles to specific groups of Accounts, so that they have different schedules and different configuration settings.
Password Checks can now occur any time within the window of time that is configured in the Check Profile. They will no longer being at an exact time of day, but rather within a time range.