How long is enough to explore Lantau, Hong Kong?

Yes, you can tour around that area on the last day of the trip. You are suggested to start off in the early morning and get to Tung Chung Station to take the cable car. After getting off, you can walk to the Big Buddha and Po Lin Monastery. 3-4 hours' sightseeing time are suggested. It won't be too rush. Notably, you need to arrive at the airport and catch the flight 2 hours in advance. Have fun!