Phil Mushnick, sportswriter for the NY Post, has made the first "official" mention I've seen of the World Poker Tour's "10:58 rule":

While the show is edited for time, its hosts encourage you to stay put as the game builds to its dramatic conclusion. Yet, most sessions can't have dramatic conclusions because one need only to know what time it is in order to know the outcome, well in advance.

Link

I first saw the term "10:58 rule" in this this post by Easy E on wptfan.com:

Uh oh, it's the "WPT 10:58 rule". I turned to my friend, who was commenting on Kirell catching the straight, and said "Alan wins with a full house". I could have BET that freeroll, without even knowing that Alan won the tournament, because it was 10:58. I KNEW the full house was coming (even though I didn't know it beforehand). I had to explain the 10:58 rule to my friend...

Hilarious. I don't think it erodes the value of the show too much, but I watch it more for the sake of watching good poker than for the suspense of who wins.