I am no stranger to overdue fines from the library. Despite all the wonderful tools and reminders available, I still manage to forget to return books or sometimes just need to keep them for an extra day or two. When I do get fines, I suck it up and pay them without complaint - I do deserve them after all. That said, I've figured out a way to avoid some of my fines (without any begging or social-engineering), and I would like to share the wealth.
When a book is returned to a Hennepin County library after operating hours, the book is checked in as being returned the previous business day. For example, whether a book is returned at 11pm on Thursday or 5am on Friday, when it is checked in on Friday morning it is counted as being returned on Thursday. So, as long as the book is returned before the library opens (the day after it is due) the book is counted as being returned on time. While this may only get you an extra couple hours in most cases, not all branches are open every day, enabling a patron to have a book for a few extra days, if returned before the library opens again.