I, too have CenturyLink fiber. I've got an hourly cron job to save the IP address of the "ppp0" interface. I've got a Linux machine doing routing instead of a modem. Since 2022-12-04, my IP address has changed 109 times. IP address usually does not change when I reboot my routing machine. I frivolously have not saved reboot timestamps.
Minimum 1 hour between addresses
Maximum 1512 hours
Mean 200 hours