rian Williams rarely has the opportunity to reveal his inner-humorist persona. Sure, there's his occasional appearance on Saturday Night Live and his guest appearances on the late-night and early-morning talk shows on which he is allowed indeed encouraged to loosen up, but mostly on his NBC Nightly News programs, he's all gravitas, as the TV writers like to describe newscasters' demeanor. Not so much on his low-rated Rock Center, something especially evident last Friday night, when Williams referred to the West Coast programmers who had moved the show around from Mondays, to Thursdays and later to two different time slots on Wednesdays. Anchoring outdoors during a blizzard, Williams described in cowboy parlance his arduous Long Road to Fridays. He told viewers, We gathered on and moved into Wednesdays at 10:00 p.m. where we were not wanted. Wednesdays at 9:00 would be more hospitable territory said the wise men in the city of angels, but they was wrong. And now, here he was on Fridays, and on Saturday, preliminary Nielsen ratings indicated that Rock Center had made its best showing in primetime to date. In fact, it outgunned ABC's 20/20 for total viewers during the 10:00 p.m. hour, nabbing 5.51 million total adults to 20/20's 5.19 million. (The ABC news magazine was ahead 6 percent among the key 25-54 age group that news programs target.) That viewer total still doesn't amount to a heap of sagebrush, however. Rock Center was down 22 percent from its lead-in, a two-hour edition of Dateline, which averaged 7.04 million viewers. Williams's NBC Nightly News regularly attracts around 10 million viewers, and in the same 10:00 p.m. hour on Friday, CBS's Blue Bloods drew 11.12 million viewers, representing a ratings blizzard unto itself.