Around 3-4 hours. That is assuming that when you reach the end you walk back via the road.
This Trace can be difficult if there has been a lot of rain lately. It's a whole different game with heavy water flow as you forced to climb against the water a couple of times.
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Really great mini gorge to climb around in. This is my personal favourite trace I have found on Yamingshan mountain. Done it a few times and seen a fair number of fish but no other notable wildlife. It isn't all that far from civilization so you see pipes and other signs of human life a few times.