They don't like to make estimates because anything could come up and slow progress so they don't want to give anyone a false idea.
Me being a rando however will make the guess that its likely sometime this month, probably in the second half. Assuming the lake trio are basically done that leaves 1 mythical (Darkrai) and 1 sub legends (Cresselia) and from previous comments and observation it should/could take a week to a week and half to do each so about 2 to 3 weeks for both.
Again that's my assumption I certainly don't have all the knowledge and it could be faster because it seems that Darkrai had been getting lots of planning which may make the process faster and smoother compared to needing to make three individual Pokémon for scenes like with the Lake Trio. Also Cresselia seems to be a fairly simple legend in comparison to the others so that could also go faster the expected.
tldr: estimates are hard but probably sometime later half this month