How long does it take after a segment is created for it to be realized? In other words, how long does it take before traits memberships qualify someone for the new segment I built?
When we are talking about Real-Time, trait qualification happens in real-time, as users qualify for a trait in their browser. Your users will start qualifying for a rule-based trait approximately 4 hours after you create the trait in the UI - Please see https://marketing.adobe.com/resources/help/en_US/aam/trait-qualification-reference.html
Note that for onboarded traits, trait qualification happens after an inbound file is processed.