In 2006 we intended to finish well into Ocotober, but we flipped to GNP from Butte and started south on Sept 15. The Park was closing down and Two Medicine station was closing, so we’d have had to go to Apgar (West Glacier) to get a permit if we’d been any later. You might be able to get a permit after Sept 15, but it would be more difficult and costly.
The other bothersome part is that the Chief Mt border station closes on Oct 1. If you finish later than that you get to roadwalk back out unless you make arrangements to get picked up. But otherwise there won’t be any traffic on the road so you won’t be able to hitch.
I appreciate the “stretch it out” part - we finished our 6 month 1999 SOBO hike on Nov 30. And wanted to turn around and start north. Our 2006 thru was just shy of 6 months. I hope yours is as good as ours were.
Jim Owen