Awesome day out there.
I started at the Ice Lake trailhead at 8:39am. I kept a nice flow going uphill to Ice Lake. From there, had an steep climb up to Matterhorn. There are a lot of strange side trails going up around the side of Matterhorn, so not sure if I took the official route, but I did my best to follow the GPS route via the maps. I got to Matterhorn Summit at 10:42am then did the out and back to Sacajawea (really gnarly ridgeline!).
When I got back down to Ice Lake, I ran into my mom and we chatted for a 10-ish minutes and took a photo (she was hiking on the trail). I then made my way back down to the Ice Lake trailhead at arrived at 1:57pm for a new FKT of 5:18:52 (including stops).
I would suggest really good shoes on the Sacajawea out and back. You're bouldering a lot and need good traction!
Note: i opted for the Sacajawea out & back to Matterhorn; however, I the previous FKT holder went down another way. The out & back adds more mileage but i think it is safer.