User blog comment:FairyRaven/Fairy Tail Chapter 368: The Third Seal, Review and Commentary/@comment-24066070-20140127014759/@comment-7418318-20140127221027

Not necessarily. If the original spell was just a "regular" shield and the time-freezing was an unintended side-effect caused by some kind of interference between Fairy Sphere and Acnologia's attack, encasing the explosion mght work.

Or if the sphere can be moved, it would also work.

But even if neither is the case and the spell would just temporarily freeze the explosion in time only to unleash it with some delay, it'd still be a great help. Because it would give the people the necessary time to evacuate out of range. The guildhall and the surrounding parts of town (or maybe even the whole town) might be destroyed, but the lives of the people will be saved (or at least some of them, depending on how much time the spell can buy).