It’s interesting that they’re doing this AU now–the winter finale. The past few “AU” type of stories have all been two hour finales so easily resolved at the end. It makes me think that the spring part of S6 will still be an AU, only righted by episode 620(ish)
Might even be quicker than that, if they’re going about doing shorter storylines sprinkled throughout the Season. It could be like Season 2, where the Cora in Storybrooke stuff was resolved within 210-216. So maybe this AU starts in 610, and ends around 614-616?