The Long Trail Side-to-Side Challenge involves completing all 88 side trails of the Long Trail system. The official trail list is maintained by the Green Mountain Club: https://www.greenmountainclub.org/the-long-trail/side-to-side/. Finishing all of the trails in one go is an interesting logistical challenge that provides a unique cross-section of the mountains of Vermont.
There is no single defined route for the Side-to-Side. The only objective is to complete all the trails in whatever order is deemed most efficient. While the official distance is 166.1 miles, any FKT attempt will be well over 200 miles due to necessary out-and-backs and connecting sections of the Long Trail. The GPS tracks submitted are from the run I (Nigel Bates) completed in 6d 10h 48m 15s starting on 7/22/20, totaling 226.66 miles with 56,947' of elevation gain. From what I could gather, this is the first successful attempt to complete the Side-to-Side in a single push. The only other attempt for which I could find documentation was made by Guthook in 2011 (https://www.guthookhikes.com/2011/06/long-trail-side-to-side-part-1-lye-brook-wilderness.html), and he did not finish, nor is it clear he intended to.
This is essentially the same thing as red-lining the Long Trail side trails, right? So if one is not local, and needs to take a couple different weekends to do it, they still could... their cumulative time would just be quite a bit longer, right? Just making sure I understand. :) I think it's a fascinating challenge! But I know if I decided to tackle it it would take me a few weeks.
Once the clock starts, it doesn't stop until you're done. One could take as many weekends as they wanted to complete all of these trails, but one would then have a total time from the start of the first trail, to the end of the last trail (in this example, that would be several weeks or months). Nigel ran all of the trails within a six-day continuous span of time; his time is not a cumulative time across several weekends, but rather a single continuous effort. Hope this answers your question!