When entering the park, is a single payment made? Can you enter at night?

You can make a payment per person of $ 15.00, also for 7 days $ 30.00 and you can also do it for a whole year $ 55.00 if you are older than 62 you can do it for life $ 88.00

Payment is a single payment yes. You can find hours of entrance in the link below but Skyline Drive is generally open 24 hours a day until winter when special times are generally implemented (Weekends from 9:30am-4:00 pm): https://www.nps.gov/shen/planyourvisit/driving-skyline-drive.htm