Campaigns, Segments, Custom Attributes

Let's say I have a campaign, and it's set up for a certain Custom Event trigger (trigger_a) and set to target a certain Segment segment_a based on a custom attribute. This campaign has a 15 minute delay built in. 

Let's say a the event trigger_a fires for a certain user, but at the moment the event fires the user is not part of segment_a. If we update the user profile with the relevant custom attribute (thus making them part of segment_a) within that 15 minute delay, will that user receive that campaign?

Or do they need to be part of that segment the moment the event fires for that user.