A lot of people have been mentioning that there are good stories that can be told in 30 minutes or less. That does not mean every story would be better if told in that time frame. For example, I would argue that the pilot episode of Aurora would not be more enjoyable if edited down to 30 or less minutes. You can tell many good stories in 30 minutes, but don't delude yourself into thinking they're the same kind of stories you would tell in a longer format.
A good metaphor would be short stories versus novels. Short story writers are not necessarily good novel writers and vice versa. In fact, the two formats very much require different sets of skills. Novel writing requires you to track a greater number of details over time and consider long term consequences. Most novel writers would probably tell you that if you want to get good a writing novels, you should practice writing novels, not short stories. Conversely, many experienced novel writers might have difficulty writing short stories. One is not better than the other, but each format has its own unique strengths and weaknesses.
As for Maurice's quote of Orson Welles, "The absence of limitations is the enemy of art," I would point out that fan productions are already replete with restrictions and limitations, such as limits on spare time, finances, experience, talent, manpower and so forth. Of all these restrictions, a restriction on how long the film can be is the single most artificial of them all. Limitations can indeed inspire artist to be more creative, but they can also lead to resignation and abandonment, especially when you have too many of them. Limitations do not create art. Artists do.
Fireproof78 pointed out that fan films need less time for world building and establishing setting because they are set in an existing franchise. While this argument has merit, the less you borrow from the franchise, the more time you have to spend setting up your setting, premise and characters. There's a reason why Aurora has a pilot that longer than most Star Trek episodes: it tries to expand the Star Trek universe by showing the lives of civilians piloting civilian starships. Because it deviates from the classic Trek formula, it has to spend more time on the premise, settings and characters. Limitations on time may encourage people to more heavily rely on the context and formula of the franchise instead of coming up with more efficient storytelling. Thus, the natural consequence of shorter films may be that, as a whole, they are more likely to be formulaic, not more creative.
