User blog comment:Omega natsu2/Chapter 413: The Book of E.N.D., Predictions./@comment-123.2.147.192-20141216052530/@comment-7418318-20141218103921

That's also how it seems to me.

From the name "magical pulse bomb" that Michello said, I originally assumed it'd destroy magic or ethernano in a big shockwave, but this looks more like it's either sucking magic in, or putting out a kind of interference field that prevents magic from being used.

Either way Christina alone is proof that the effect is incremental rather than instand, since they talked about how their magic reserves were getting low very quickly and they'd soon lose the ability to keep in the air.

With Dragons having so much and so strong magic, it'd make sense for them to last longer than Humans.

But come to think of it.... could it be that this sucking in of magic isn't the end-effect yet, but a kind of charge-up sequence?

What I mean by that is, that unlike the prime Face that Wendy and Carla destroyed, maybe the other Faces don't have a sufficient integrated power-source and instead they need to leech magic from their surroundings until they reach critical mass and blow up to achieve their full effect.

Since Kyouka was able to speed up the countdown it's unlikely that this first countdown was the charge-up, since it's doubtful that she could give provide all 3000+ Faces with energy and fight Erza at the same time, so my money goes on Kyouka fiddling with a countdown that would start the charge-up, rather than finish it.