If you only have three days, I would rather make the route feel doable than make it look impressive on paper. In Zhangjiajie, pacing and sequence matter more than squeezing in one extra name.
Arrival day is better for landing, settling in, and understanding your transfers than forcing the hardest attraction immediately.
For most visitors, this is the one day that deserves the most complete block of time.
If your departure window is tight, be conservative and avoid letting the final day become a race.
If I were helping friends on a first trip, I would usually keep day one light for arrival, use day two for the National Forest Park, and use day three for Tianmen Mountain if the departure timing still allows it.
The logic is simple: put the largest, most time-hungry experience in the middle, and leave the uncertain arrival and departure edges with more breathing room.
This version suits first-time visitors who want the classic scenery without turning every day into a rush.
If you want slower photography time, or you are traveling with parents or kids, the right move is usually subtraction, not expansion.
When weather looks unstable, I usually protect the main day first and reduce the optional filler. When the return is tight, I avoid putting the most queue-sensitive and weather-sensitive item at the very end.
In a 3-day trip, the most valuable thing is not maximum coverage. It is keeping risk and stress inside a range that still feels enjoyable.