Schon is used more frequently than its English equivalents. It is often used to emphasize agreement or the earliness of an action. With reference to the passage of time, the opposite of schon is erst. While schon emphasizes how soon something will happen, erst emphasizes how long it is until something happens. Thus schon in drei Wochen means "in only three weeks [and I'm glad I don't have to wait longer!]", while erst in drei Wochen means "not for three weeks [and that seems so far away]".