We've had the same experience! This is because OverDrive counts the 21-day checkout period as 21 x 24 hours (or 504 hours from the moment it's checked out). Sometimes the "one day left" really means "expiring today," which can be confusing.
To find out how many hours you have left, sign in to your account on FVRL's OverDrive website or tap "Add a Title" from the Bookshelf in the OverDrive app, then go to your Loans page and look for your book. You'll see how many days/hours remain until expiration displayed across the top of each book. In the Libby app, find the title on your Shelf and look to see where it says, "Due in [#] hours."
However, if you believe you didn't get your full time, please let us know, and we will contact OverDrive to investigate what might have happened.
If a book has already been checked out to the next person, we can't override that and check it back out to you. But we can put you back on the hold list for it if you let us know your library card number and PIN, as well as the title and author of the book you want to finish reading.
Still having issues? You can Get Help Using FVRL's Online Resources.