I'll be firing up a test in the near future and on the same day we will be activating an Audience based upon a custom Mbox parameter
My question is, does it take time to build up this audience, or will Target know to include the visitor right away upon page load ?
The order of actions in Launch are
Load Target > Response Token Listener > Add Params to All Mboxes > Fire Global Mbox
As a hypothetical, let's say we want to only include logged-in users
Alandy_Iceboats Target audiences are considered real-time audiences. So you should see users qualifying for the audience as soon as they satisfy the audience criteria .
Here's a document that gives you a quick overview on the different audience options in the experience cloud.
Audience creation options in Adobe Experience Cloud