I'm thinking March 24, 1989 was the last time a minimum of three straight hours were offered on network programming on a regular basis. All times Eastern:
10am on NBC $ale of the Century with a special guest appearance by President Bush
10am on CBS Family Feud
10:30am on NBC Classic Concentration
10:30am on CBS Card Sharks
11am on NBC Wheel Of Fortune
11am on CBS The Price Is Right
11:30am on NBC Win, Lose or Draw
11:30am on CBS the second half of The Price Is Right
12noon on NBC Super Password
12:30pm on NBC Scrabble