Thank you for your review and observations.

We'll fix the display of the hard to read intervals. It's true that it's difficult to understand what 525600 minutes stands for. :)

We have noticed that a lot of people who used a different reader before have their subscriptions as Live Bookmarks. Unfortunately the Firefox WebExtension implementation does not let you read Live Bookmarks via the API which makes it impossible for the add-on to use or to import them. We are hopeful to see a change in the API but this will most likely take some time. See Bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1418257

Unfortunately there are some feeds that don't follow the rules or behave in somehow peculiar manner. Usually the best option is to notify the feed provider that they should fix the feed rather than trying to fix N different readers to deal with their problems. If e.g. feed posts several articles with the same date stamp and you still want to see notifications, how should the reader behave? Show just the first? Show none? Show all but with larger intervals in between?