I do not use the cloud/API data, so i have no insight to offer.
A quick search for “data buckets” revealed this 2018 thread. It is for the older Air/Sky devices, but should mostly still apply to the Tempest (which combined the Air and Sky into a single unit).
https://community.tempest.earth/t/data-archive-buckets-explained/1063
I vaguely remember a more recent thread on the buckets and retention, but didn’t save it because I have no interest in the cloud/API stuff and only work with the local UDP API stuff…