Brief report:
I started up on the hiker's trailhead (elev: 100 ft) at 9:15pm at the corner of First Avenue and Monroe Street in Seward. The first few hundred feet in the forest are great. It reminded me of those gnome cartoons with everything green, fearns, moss, etc. Then, I took a wrong turn and ended up hiking some trail that leads to the northeast ridge to Race Point (elev: 3,022 ft). The true summit of Marathon Mountain is more technical and sits at 4,603 ft. I reached Race Point at 10:28pm. Took pictures and rested there for ten minutes. Then, I came down via the Racer's trail that ends up at the end of Lowell Canyon Road/Jefferson Street. Was back at the hiker's trailhead by 11:18pm. Amazing that you can hike in daylight even past 11pm in summer.
Additional info about climbing Marathon Mountain can be found here.