Concerning the backup not being updated, I think updating to master might fix it. I have pushed some fixes to our backuper lib in the last weeks.
Concerning the other issue, I just pushed a fix:
https://github.com/discourse/discourse/commit/67ec81babfde3942a9120182c87d74201fb83596
This commit will also now display last_backup_at and last_updated_at in the user timezone which I think is better in this case.