A question for you to ponder: if the dining halls are open for dinner from 5 to 7:30 pm, when is the best time to go to avoid the crowd?
The first answer might have something to do with when people get hungry, and you would go through when you actually have dinner, if your dinner time represents a majority of people's. Since not a lot of people eat dinner at 5, most eating 6:30 or later, before 6 is probably a good answer.
Which is true, and I congratulate you on your reasoning. But then I don't always feel like eating early either, and it's pretty annoying if you get hungry again later at night.
It turns out that when the dining hall gets crowded may not be entirely determined by when people get hungry, but also by when people think they'll go get food. If you accept the solution that people like to eat with their friends (which is mostly true), then there's also the problem of how people decide when to go and get food as a group. Think about it. If you're meeting someone, are you more likely to say "I'll meet you at six", "I'll meet you at six thirty", or "I'll meet you at six thirty seven"?
The point is that when people say they'll do something together, the time they choose then to be short, and some how more memorable. The o'clock on the dot is easiest (and shortest) to remember, then the half hours, the quarter hours, and maybe the five-minutes. So a good time to get food would be a short time before any of the easy to remember times, say 6:25 or 6:40.
If only I had the same sense of understanding of buying practices in the stock market.