A bit of research and I have answered my own question.
The 1981 U.S. GP-West II in Las Vegas was held on Saturday. A brand new circuit, it was one of the first GPs to circumvent the rule that a race had to be held on the circuit before a GP was. Perhaps t was the first GP held in that regard. Practice was held on Wednesday with qualifying on Thursday and Friday. I was there that Wednesday, waiting for the circuit to open. I kid you not, there was a woman sitting behind a card table at the entrance to the pits. "Carlos Reutemann? Oh yes, I see your name listed. You can come in." Unbelievable but true.
it turns out that the British GP for a while alternated between Saturdays and Sundays in concert with the odd-year Silverstone/even-year Brands Hatch venue alternation, and even including the the two GPs held on British soil in 1983:
Up to and including 1975: Saturday
1976: Sunday
1977: Saturday
1978: Sunday
1979: Saturday
1980: Sunday
1981: Saturday
1982: Sunday
1983 GP of GB: Saturday (Silverstone); GP of Europe: Sunday (Brands Hatch)
1984: Sunday
1985 Both GPs/venues: Sunday
1986 and on: Sunday
Funny how you forget things, seems like Sunday F1 has always been around , but its not, I would have watched the races on a Saturday.