It is a really bad hint. In fact it is dead wrong. If you move up to the next era
before GE starts, you will have to face challenges based on the new era, not the old. As far as I know this has been true since GE started, so I don't know where
@Zeidy Z got the wrong information. You should move up to the next era right
after GE starts. Then you will get to face the old era's challenges all week, giving you that time to progress in your new era before having to face the new era's challenges. During that week, your GE rewards will still be from your old era, but if you have a Temple of Relics, any rewards from it will be from your new era.