User blog comment:B214/Chapter 501: Mari and Randi/@comment-29874610-20160912144506/@comment-25395791-20160912144801

I'm not quite certain about that. Zeref showed before that he's able to stop time for a brief moment as well (well, kinda.....when he killed Zancrow). Other than that, since he hails from the ancient Mildian, it's not all that implausible that he isn't capable of stopping time on his own