Topics get repeated and if it's too soon, it's frustrating to see on a forum. How long in between do you think is best for a topic to die out before it's started up again in a new thread (by another member)?
It depends on how fast the forum moves, I think. The internet is full of repetitiveness, and it's hard to control it at times on fast-moving sites. I wouldn't even consider it a big deal for sites that move so fast, especially if the topic hasn't grown very large. As for a specific time, I think there are too many factors that could lead me to combine or close a repetitive topic. If the topic is on the first couple of pages, how large the new topic has grown, or how relevant the topic is, could all be contributing factors in combining/closing duplicate topics.