24 hours later and I finally have a message telling me that there is "About 32 hours remaining".
When I go to General->Usage->Storage->Manage Storage it twlls me my backup size is 4.8 GB. Presumaby, much of this is already backed up, so a current, incremental backup should be much less than this. (I have 17.4 GB available iCloud storage.)
How can it possibly take 32 hours to do an incremental backup and why did it take 24 hours to calculate that amount?
Still no success, but I think I understand what's going on....
Every few months I go on a dive trip. During those trips I am away from the mainland and away from the Internet for five or six days at a time. Also during those trips I transfer many gigabytes of photos and videos from various cameras to my iPad.
My guess is that when I finally have a WiFi Internet connection again, iOS simply cannot cope with the huge amount of new data that needs to be backed up to iCloud. So, it fails without issuing any sort of meaningful error message.
Any idea how I can report to Apple this serious flaw in iOS iCloud backups?