Thanks for the hotel advice.

And to alleviate any pronoun confusion, I'm a "he"

When I said Forbidden City will be closed, I meant that I will be getting to Beijing late enough in the day that it will be closed for the day, so I will not be able to enter. The website I looked at says the last entry is at 16:10, and my flight from Hong Kong is not scheduled to land until 15:15, so I don't think that's an option on day of arrival. I also am seeing that even though the park at the Temple of Heaven is open late, the "main attractions" there close at 17:30. The same website (https://www.travelchinaguide.com/) says the Summer Palace closes at 18:00 but the scenic spots close at 17:00

So do you have any suggestions for an early evening excursion, if I am going to stay at the St. Regis?

Or should I consider hiring someone to meet me at the airport and take me to the Great Wall (or somewhere else?) and then take me back to the hotel that evening, and then spend sunday in Beijing proper?

My (domestic) flight leaves Beijing at 20:00 on sunday.