User blog comment:B214/Volume 22 spoilers/@comment-29778526-20170126060633/@comment-9595671-20170128043219

Remember, that's just how long the barrier itself will hold. They won't have to worry about that if they get a more permanent solution within that timeframe.

It's likely not gonna happen in the next thirty as EX has heavily implied, but they'll probably be out before the barrier's time limit runs out. Also I don't think time wouldn't count in the barrier, that would make the fact Issei and Ajuka talked to some of the group while they were still inside very hard if not impossible.