Yes, tradition would say that certain obvious times are best for being bumped. Friday afternoon/evening, Sunday afternoon/evening, early Monday morning (when many business travelers fly), etc. Saturday is generally one of the least heavily booked day of the week. I don't know what your best chances would be for mid-week travel. E.g. always a early morning flight, etc??? Other good opprotunities, though less predictable of course, involve equipment swaps (smaller plane used), or the day or period after a major weather or other situation which requires many people to rebook. I too would appreciate knowing of any patterns people see out in the field on which flights are overbooked. I too find a lot that flights will be over by 10 or 15, and they will not need volunteers. It's best if it's 20-plus people overbooked and you are first in line.