TL;DR: EA Global meetings have a default time, but you can skip to the goal of the meeting and avoid the urge to fill the entire allotted time.
Background
I had a meeting with Lizka. It was 7 minutes. In the remaining time, we grabbed food, and decided to write this post together.
What was in our meeting?
Me: “How about adding [some mysterious feature] to nudge people to write summaries for their posts?”
Lizka:

Me: “We have time left, wanna write a post called EAG Meetings Can Be Short?”
Lizka: “Can we have an image in there?”
Main Takeaways
EAG meetings can be short, have images, meta jokes, and have a concrete result, such as something new posted to the Forum.
Related Reading
You can also help make short meetings happen by saying, "I'd love to talk about X. I think it'll probably take about 15 minutes, but I'm happy to meet for the default half hour if we find we have more to talk about!"
HOWEVER if you offer a shorter meeting like this, make sure you do actually give your interlocutor a chance to gracefully exit after 15 minutes. They'll be grateful you kept to your word!