There are two things you can manage on this page, Time Sets, and Date Ranges.
Time Sets
While you can easily create Time Sets by way of setting Open Hours in a Map Floorplan, you may want to manually create time sets for more advanced purposes. Generally it is advised to use the Open Hours on the Info tab on the Floorplan when setting hours for a lab space or similar. When you create a time set by setting Open Hours, they are automatically tied to the Division. If you create a Time Set in this Settings page, it will NOT be tied to a division unless the Name of the Time Set is identical to the name of a Division.
The more common use case for making a general use time set is something like "Business Hours" that are not tied to a specific Division/Floorplan but rather an organizational concept that you could apply on the fly to any given Report.
For more details see Time Sets in KeyConfigure.
Date Ranges
The more common use case for this page is create Date Ranges. These are used in Reports, so it's more convenient to have a preset than use Custom on a regular basis. As you're hopefully aware in building a report you can choose things like Trailing 30 Days or Last Month. If you need presets for things like FY 25-26 or 25-26 School Year you can quickly create those here, and then have one click choices in the Report builder instead of manually picking those custom dates all the time.