Darcy Piceu set the women's supported FKT for the JMT in 3d7h57m (3d4h12m from Whitney Summit), NoBo, September 15-17, 2017. Piceu's trip has an asterisk since she didn't follow the official JMT route from the top of Nevada Falls to Clark Point, but rather went down the Mist Trail, then crossed the Merced River and climbed back up to Clark Point. She was off the official JMT for about 1.3 miles, but her route was probably slighly longer than the official route, and almost certainly slower due to the technical nature of the Mist Trail and the several hundred foot climb back up to Clark Point. While the runner is responsible to know the route, and this is clearly a mess up, it doesn't seem severe enough to "disqualify" her from the FKT, especially given that she beat Sue Johnston's time by 12 hours! Piceu had only 3 sleep breaks of about 1 hour each, plus several "10 minute dirt naps". Her trip was followed an discussed below (pages 11 and 12 of this thread, and on the backpackinglight.com forum, is summarized in a nice article on running.competitor.com, and chronicled in a blog post by one of her crew people, Jeff Kozak (including splits).
south to north
3d 7h 57m