Segments may update immediately or periodically depending on the scenarios. Below are use cases on when a segment will it's members.
Segment is Created/Updated
When a segment is created or updated, we will automatically update its membership in the background. Depending on the number of contacts you have in your account, it may take at least a few minutes for our system to evaluate segment members.
Contact is Created/Updated
Whenever a contact is created or updated, we will also reassign segments for that contact.
Membership Update Interval
Segments will update eligible members every 12 hours. This means that for segments that use datetime conditions like "less than 5 days ago", there may be 12 hours delay in evaluation.