I'd figure 4 -5 hours unless your group is all good skiiers and in really good shape. You're on climbing skins pretty much all the way to hut past the Fulford Cave campground area. Assuming you aren't navigating in a snowstorm, and the tracks are there from previous skiiers, route finding is pretty straightforward. If you can't see old ski tracks on the trail though, I agree with the other poster that it may be difficult to see the blue diamonds. There is a false trail going off to the left just past the Fulford Campground area (called "Pack Trail" on the 10th Mountain map), paralleling Brush Creek. It had fresh ski tracks when we skiied in last winter and we briefly considered giving it a try before we saw the blue diamond ahead in the trees. Ignore the false trail, and go straight ahead into the trees.
There is another trail junction at the Hat Creek drainage. We found an alternate trail to the hut during a day ski. From the Hat Creek drainage trail junction you can follow the summer road to the hut (shown on the 10th Mountain map, just west of the main trail). It had been groomed by snowmobiles, and was easy to ski on. It's a lot less steep, and we were able to skip some steep sections approaching the hut and didn't need climbing skins.
FYI - we skiied down the Hat Creek trail on the return trip from Estin to Yeoman Park. There wasn't much snow on Ironedge, and looked like it would have been a luge run down. Hat Creek was a much easier ski down. There weren't very many blue diamonds at all on the Hat Creek trail, but there were ski and snowmobile tracks, and route finding was pretty easy.