Airport Money Changer in Guangzhou Airport

I'm afraid the money exchanges has been out of service then. Its service time is from 08:00 to 21:00.
Actually, you have two choices from the airport to your hotel.
One is to take the shuttle bus line 6 to Tianhe Terminal of Guangzhou Airport (CITIC Plaza), close to East Railway Station. After that, you can walk to your hotel. It is very near. The service hours of the shuttle bus is from 06:30 to the arrival of the last flight.
The other is to take subway line 3. But you need walk to Airport South MTR Station first. The subway line 3 can take you to Guangzhou East Railway Station. Then you can walk to your hotel.

For money changer, you can take a taxi to your hotel. Some taxi driver can accept USD. If they dont't accept, You can exchange your money at your hotel, then give RMB to taxi driver.