There's no ETA announced by dev yet, since the implemention of next update is still on early stage of development.
I personally guess the next update needs at least 5 months to be flawlessly implementated.
Viewing post in (WIP) Hailey's Treasure Adventure(+18) comments
I speculate by looking at the amount of work needed to be done for the next update,
There are about 5 images needed to be done, maybe 5 more sprites needed to be drawn.
Furthermore, the language mod system that needs to be tested.
I tried 2D animation once, its very time&mentally-consuming. So I can roughly speculate on how much time is needed to put on this art project based on complexity of the artstyle.
Still, just a rough speculation of my own, take it with a grain of salt.
Hm understandable, but.
Last two major updates had same amount of levels and other stuff.
What I mean time from 0.4.5 (2022/02/09) -> 0.5 (2022/04/21) (so 71 days)-> 0.5.4 (2022/07/10) (so 80 days).
Both added 4 levels, 0.5 three new biomes, 0.5.4 two new biomes. 0.6 add also 4 with I guessing two new assets palates for new biomes.
Both added 3 enemies, 2 old and 1 new. 0.6 adds 5, 3 old, 1 new and one special variant. So here is potential for some extra work and time to be considered.
There was 2 new pictures in 0.5 and there is 5 new in 0.5.4. 0.6 has 7 new planed so also some extra work.
Technically setting up language settings isn't that hard. It is just testing if all places where it was hard coded in it will use text document instead.
What I'm trying to say is I don't see that of a significant of a increase in work goal. To warrant extra 60 days of work in compartment to previous updates. I basing it also on my personal knowledge with 3D, not same but comparable.
So I just kinda hoping to see next update mid to late September. Instead of your predicted November.