While I cannot point you to an Internet link. I have personally observed both Grey's in the wild and wild caught, as well as domestic bred pairs in Aviary situations. Greys do not seem to require the often recommended 10-12 hours of sleep.
Both in the wild and in the aviary, there is much chattering going on after dark, for quite sometime. The chattering resumes very early in the morning before the sun comes up.
In 1992, I spent 6 weeks in West Central (Equatorial) Africa. Two of those weeks was spent on safari following a wild flock of Grey's in Ghana. My observation over that two weeks, based on when the chattering stopped and then started again, was that the amount of actual sleep they get varies from night to night. Some nights it was 6-7 hours, others it was 7-8 hours and on occasion it was close to 9 hours. Of note, is that Grey's both in the wild as well as in captivity, do nap. My own CAG takes several naps throughout the day. The breeders in the Aviary also nap several times each day, and Grey's in the wild nap during the day as well.
In addition, we had nest cameras and microphones in our aviary for many years. I observed the same sleeping patterns with breeders in captivity.
Combining these observations with the fact that my own CAG has been on 'my' schedule, (which averages, lights out between 10:30-11:00pm and breakfast at 6-7am, for all of her 12 years, with absolutely no ill effects; I would say, based on my observation and experience; that while individuals may vary, the 'average' African Grey, on average, requires between 7-9 hours of sleep each night.
Just my own personal observations and experience.