There are two normal approaches to summit this mountain and I have done both. The first is from the Flowed Lands camp spot (a 23km/14.3 mile hike with 4100') which I first hiked back in 2012, or from the Upper Works road which we chose to do on this day March 31st, 2018.
Allen Mountain Stats from Upper Works Road:
Total Ascent: 4062 feet
Time: 10.5 hours (March 31st soft snow conditions)
Within a few minutes of leaving the parking lot you cross the Hudson River over a rickety metal bridge. Soon after, you will hit Jimmy Lake. Commonly crossed in the winter months as a shortcut, we decided on March 31st, 2018, that the water pooling on the top of the ice meant that we shouldn't chance it and take the 0.5km/0.3mile detour around the lake to get to the other side. Soon after you will pass the turnoff to the McAdam's Fire tower hike and then you travel on flat trail passing a few lakes on your right. At the 4km/2.5mile mark, you get your first glimpse of Allen when passing a small swamp.