It seems as though, at least on the 767, there have been more lines with fewer than 17 days total. Some with as many as 15 or 16 days off. However, due to the fact that these months are usually built as 4-5 small trip pairings, with only 4 days "off" in between, if you take the increased number of commute days into consideration, you'll likely be gone from home for more total days than you would for a conventional 17 day trip. Additionally, these lines also only pay min guarantee. Still, they could be nice options for those who live in base.