Zhangjiajie National Forest Park in 1 day

The cable car ride to Tianzi Mountain takes about 8 minutes for one way and the Bailong Elevator ride only takes several minutes, but there might be a long queue for elevator. I think it is no problem to visit the places you mentioned within 6-7 hours. There is a path between Tianzi Mountain and Halleujah, you can take shuttle bus between these two sites and the ride takes around 20 minutes. You can see monkeys at Golden Whip Stream. I don't think there is still time to go to the Grand Canyon after the National Forest Park in the day. It needs at least one day to explore the park and another half day to visit the Grand Canyon, so two days will be needed.