User blog comment:IamJakuhoRaikoben/Chapter 368: The Third Seal, Review./@comment-5598380-20140124212807/@comment-7418318-20140125110945

We neither know how and why exactly Fairy Sphere caused this time-freezing and we don't know how this bomb Lacrima works, so it's impossible to tell if another timeskip might happen. Though I guess if it happens, it's going to be much shorter, since the difference is between vaporaizing a guild or an island. Maybe something around a few month.

Be that as it may, there's another big problem with that spell. Mavis was only able to cast the Fairy Sphere the first time by using the combined magic from the hand-holding FT mages (plus Laxus - he wasn't in FT at that time). That means for her to save the guild with the same spell again, the FT mages would need to get enough advance warning for them to join their magic together for Mavis to use to feed the protective spell.

But if she used it, I think it'd be smarter to encase the bomb lacrima rather than the mages (assuming that the spell blocks all transfer in and out, rather than just preventing magic from getting in). If the explosion happens inside the sphere it wouldn't just protect the mages, but also the building and more importantly innocent bystanders outside the guild hall. If the bomb is as strong as it sounds, it's bound to cause collateral damage to the rest of the city too.