What's the rule??

What's the rule?? On college extra points when you score a TD at the end of the game (Zero time left on the clock)? I saw a couple of games earlier in the year where they brought everyone back to kick the extra point. Last weekend in the LSU / Tenn. game there was no extra pt attempt after that end of game fiasco. I never know when they are going to attempt the extra point. From what I've seen the last few years it seems to be up to the whims of the officials. Obviously spreads and totals can be impacted. More often than not it seems they don't attempt the kick unless it's needed to tie or win the game.
The kick is supposed to be tried so far as I can tell, but if the team elects not to kick it, it is considered a miss and the game ends. I believe the officials always give the option, but often team declines.
I believe the rule was changed a few years ago to specify that the scoring team has the choice to attempt the XP or not. Before that they were always supposed to run a play, but sometimes the officials just let everyone run off the field anyway.
Thanks for the responses. That seems consistent with what I've been seeing.

I hate to tell you how many times it's killed the pointspread.
it was my belief that if the extra point would have no impact of the final outcome of the game then the try for the extra point is waived. i wasn't aware that it was up to the discretion of the scoring team.
[QUOTE=tvrw34243;29392]it was my belief that if the extra point would have no impact of the final outcome of the game then the try for the extra point is waived. [/QUOTE] You were right to believe that and I stand corrected. This is from the NCAA's 2009-2010 rules: [I]If a touchdown is scored during a down in which time in the fourth period expires, the try shall not be attempted unless the point(s) would affect the outcome of the game.[/I] I don't know when the 2010-2011 edition will be available for download, but the 2009-2010 ones can be had here: [URL="https://www.ncaapublications.com/productdownloads/FR09.pdf"]https://www.ncaapublications.com/productdownloads/FR09.pdf[/URL]
Thanks for doing the research! Not 100% sure that's consistent with what I've seen but I'll be paying attention going forward to see how it's enforced. It happens almost every week.