In Fairy Tail episode 287, Zeref, talking to Makarov, mentions that 10 years ago he stopped the invasion ten years ago (from the time of the episode) was a mistake and Zeref stopped his Empire because it was not yet time.
However, from that time point, one year ago Fairy Tail dissolved, and Zeref left Tenrou Island only eight years ago.
I haven't read the Manga, so it would be good to know: When and how did Zeref enter Tenrou Island, and if he was there at the point the invasion started, how did he stop the invasion?