User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-4933386-20151207132837/@comment-24039250-20151207133414

Acnologia didn't travel to the future. He's just been waiting just like Zeref. Anna is likely Layla's Great-Great-Grandmother and left instructions for her descendants to open the gate when Magic was at its best, which was X777. There's probably more to it but we will find out later.