This is a terrific route! Great mix of hilly and rocky ascents and descents but also some very runnable sections. It was a scorcher in Philly today (maybe 95F?) but the trail basically was manageably cool-- probably never got over 75 until the last 30 minutes where it was probably 80 degrees by the time I ended around 11AM. But the course is a bit hard to follow. I recommend anyone attempting this that is not already intimately familiar with the course to watch a navigation method closely. I got off course several times because I didn't watch closely enough-- even though I had my phone in my hand the entire run. I think the distance is closer to about 22 or 22.5 miles.
The Wissahickon trails are a gem of Philly. Probably one of the best urban trails in the US! What an amazing resource for this region!