Your comment about there being no ratings at night was not one I would concur with. Williams had a huge audience. I was a regular listener and never fully appreciated how big his audience was for an evening program!
He may have had the largest night-time audience in Sac, but whether he did or didn't doesn't change the fact that night time radio has little effect on a station's revenues or overall audience.
As far as KTKZ's numbers are concerned, I don't know how specific day parts show up, but overall, KTKZ was running behind KCTC, as a Music of your Life station, and now as Air America.
As I said before, KFBK is #1 because of Rush. The only thing the PD has to worry about is whether or not the balance of the programming is good enough not to drive listeners away.
To prove the point, most stations are driven by the morning show, with the total audience declining as the day goes on. But practically from the day he started on KFBK in 1984, Rush's show has consistently outrated the morning news.