The route from the Edelrauthütte adds 2 - 2.5 hours to the normal route from the Hochfeilerhütte. On my way up, I only took a short break at the Hochfeilerhütte, for I wanted to be up there rather sooner than later, in case the weather would turn bad. On the summit, I still got some views, though the clouds were already building.
Soon after I started my descent, the summit was hidden in the clouds, though later it turned out to be false alarm and the summit became visible again. Despite threatening skies I made it back to the Edelrauthütte before the rain came.
From the Messner Biwak. Indeed, the approach from there is quite tiring. The face itself was in good/easy snow condition. The descent was difficult due to a wrong turn in the Glider valley floor taking the winter route (you need to climb up 200 meters on the left because the valley pinches down to an ice cliff around 2000 meters).