There is some latency between entity.attributes being seen in an mbox request from a page and it being available for delivery by Target. This not usually very long, Shruthi's linked doc discussed it. Furthermore, you'll notice a longer latency for those entity.attributes getting reflected in the Recommendations catalog search UI.
The catalog search UI latency should not prevent you from creating a collection though. If you know what the new value is you are trying to create a collection around, you should still be able to define the rules in the advanced search and save it as a collection. You may not see any results yet, but the collections should still be valid.