All pages involving display of multiple properties are sorted (unless otherwise specified in the Advanced Search sort by choices) by the 'Calendar Last Updated' and 'Rates Last Updated' timestamps. Calendar updates take precedence over rate updates and a randomizer is applied where dates are the same for multiple properties. So in summary properties that most recently updated their calendar and rates will be near the top.
Calendar Last Updated timestamp is updated every time a booking is manually added to your availability calendar. Where you have an iCal file linked four times daily a batch process is run on the server. How this handles 'Calendar Last Updated' is to compare the iCal file with what's in the availability calendar in WHPR for the property, if there is any delta (add, update, delete) it updates the 'Calendar Last Updated' timestamp.