Board Thread:General Discussion/@comment-24382631-20140105033403/@comment-4957813-20140105041652

The length of time depends on who is wielding the Bankai. The greater the Reiatsu of the wielder, the longer he or she can maintain it. However, once they run out of Reiatsu knocked unconscious, or if they will it, then the Zanpakuto will revert back to its sealed state.