Is Mount Emei enough for one day?

You can only visit some scenic spots in a day. If you have more time, I suggest you swim one more day. I'll give you some itineraries for a one-day tour, which you can refer to:

The first trip: from Huangwan Station, take the scenic spot sightseeing bus to Dongleiping parking lot, walk to Jieyin Temple, take the cableway to Jinding, visit the ten-square Pu Xian statue of Jinding, the three halls of Emei Mountain, visit the Snake Cliff, observation deck, see the sea of clouds and overlook Gongga Snow Mountain, then return to Dongleiping parking lot and take sightseeing bus down the mountain.

The second trip: From Huangwan parking lot to Wannian Temple parking lot, take Wannian Temple cableway to see one of the top ten ancient scenic spots in Emei Mountain, namely "White Water Autumn Wind", Pingzhuan Temple and Mount Emei Mountain Treasure "Pu Xian Riding an Elephant Bronze Statue", then walk to Qingyin Pavilion, visit Bailong Cave, Qingyin Pavilion and "Shuangqiao Yin Qing", visit the first-line sky and Heilongjiang plank road, and enter Emei Mountain Ecological Monkey Zone to watch monkeys.

Your time is tight. I suggest you book tickets, sightseeing tickets and ropeway tickets on the travel website before you go. Then you can take your ID card directly to the self-service machine to pick up the tickets, so you don't have to wait in line to buy tickets if you can. Wasting time,