Zhangjiajie is not a day trip from Changsha — give it two nights

The sandstone pillars are three hours west, the park is huge, and the Bailong lift and cable cars are separate tickets from the entry pass, which is real-name and valid for several days.

Sleep in Wulingyuan at the park gate rather than in Zhangjiajie city, go up on the first shuttle, and keep the crowded viewpoints for the late afternoon when the coaches have gone. Fog is common; two days gives the weather a second chance.