Animaniacs never aired in primetime on the FOX network. On the other hand, according to my calculations, Tiny Toon Adventures aired at least 7 times in primetime on FOX. Also, Animaniacs did air in primetime on the WB on December 31, 1996 as part of the Kid's WB! New Year's Eve Jam.
Since you brought up a show premiering in primetime, these are the only Fox Kids shows that premiered in primetime on the FOX network: Taz-Mania, Batman the Animated Series, Life With Louie, and Goosebumps. Tiny Toon Adventures also premiered in primetime, but it was on CBS. Remember, Tiny Toon Adventures originally aired in syndication from 1990 to 1992 before airing exclusively on the Fox Kids Network from 1992 to 1995.
To the best of my knowledge, Pokemon never aired in primetime on the WB. It did, however, air in primetime on Cartoon Network starting in the fall of 2002 along with Yu-Gi-Oh!. I believe this would have been the first time that the show aired in primetime on any station in the United States since prior to this, Kids' WB! had exclusive airing rights to the series after it left syndication in early September 1999 (it aired in syndication and on Kids' WB! from February to September 1999 and only in syndication from September 1998 to February 1999).
Although no episode of Pokemon aired, there was a primetime special about Pokemon the Movie 2000: The Power of One on July 16, 2000. Additionally, there were special previews/commercials for Pokemon that aired during 7th Heaven in 1999. The premiere of M2M's 'Don't Say You Love Me' music video and the Pokemon League Games preview are two that instantly come to mind.