Two hour rule
The Annual Interactive Fiction Competition's "two hour rule" states:
Judges must base their judgement of each game on at most the first two hours of play. If a judge is still playing a game at the end of a cumulative two hours of playing time and wishes to continue playing it, the judge must rate the game and not change that rating later before continuing play. Authors may write a game of any length they desire, but should keep this rule in mind when determining the length of their entry.
Also from the IF Comp's web site:
There are a couple of things which you need to keep in mind when writing your game. Judges will only have two hours to play your game; if you write a long game, many people will not see parts of it. In addition, given the competition's purpose to encourage short works of interactive fiction, many judges rate overly long games poorly.
The Rule: The text adventure you enter must be winnable in under two hours. Judges will be asked to rate it after playing for that long.
That's the main point of the competition. You don't have to enter something really long to have a chance at winning, because you aren't allowed to. That way we get more entries.
The rule is not debatable. It's the only rule, and it's not very unreasonable.
Long-time members of the IF community tend to believe that when exceedingly long games are entered into the IF Competition, it violates the spirit of the competition, though not the letter of the law. The attitude among such people is that while longer games are desired, they do not belong in the IF Comp. Thus, exceedingly long games have generally not fared well in the competition, with one or two exceptions.
Over the years, many people in the newsgroups have questioned the two hour rule, but none of them have so far changed the consensus of the IF community.
Also note that the Spring Thing exists in part to offset whatever disadvantages there may be in the two hour rule. The Spring Thing is a competition that encourages longer games.
Discussion about the two hour rule
(The following is an exceedingly incomplete list. To find many more discussions of this type, you may search Google Groups.)