Since WLS in Chicago stripped an hour of news at 6 p.m. weeknights, "MG PM" aired after the Sunday movie and the local *and* network late news (this was when ABC did a Saturday and Sunday night 15-minute late newscat) and was later joined by the second airing of "Squares." (The first airing ran in "LMAD"'s old Saturday at 6:30 p.m. slot.) The reason I don't give exact times is that back then, "The ABC Sunday Night Movie" frequently ran over 10 p.m. CT.
It wasn't that barter *wasn't* being used in prime access--a lot of the less successful variety and scripted shows like "Stand Up and Cheer" and "Simon Locke/Police Surgeon" were barter, as was the more successful "Mutual of Omaha's Wild Kingdom," Lawrence Welk and "Hee Haw." It's just that for the most part, game shows remained all-cash ("The Movie Game" and "Sports Challenge" were the only barter games in syndication that come to mind). What changed things was the development of "cash plus" in the 80s, I believe created by Paramount for "ET," where the station pays *both* a license fee and holds ad time for the syndicator. That has become SOP for almost every strip syndicated series, with the once-a-week shows almost entirely barter and the only series going all-cash being the "I Love Lucy" and "Honeymooners" reruns at 2 a.m. when the station's not running infomercials.