The GitHub workflow runs at schedule to check update, build AppImage then publish.
Stable: once every week Sunday (7:00 AM UTC)
Preview: twice a day (12:00 PM and 12:00 AM UTC)
Beta: with recurring 3-day cycle (8:00 AM UTC)
All traditional distros take some time to push new updates. Even the bleeding edge Arch isn't close enough to getting Calibre latest:
https://archlinux.org/packages/extra/x86_64/calibre/ I think the current cycle is good enough.
If you think more faster updates is necessary or face any issues related to AppImage builds please report at developer's repo issue tracker.