Jeez people... it did NOT take 18 months for them to develop Mistlands...

It took 18 months for >>> Game-Stability fixes... H&H... food system/ stam overhaul... added POIs, such as caves and tar pits along with new creatures/ recipes/ resources/ armors/ building parts, etc.... and THEN Mistlands.

This was also during covid (working remotely), and "growing pains" (adding new staff), and all of this is custom-made (no purchased assets).

According to the devs (via the update news), they worked 9 months on Mistlands, so it's (probably) safe to assume it would be similar (9 months) for each of the remaining "land biomes".

Who knows, when it comes to "Ocean".... no clue what changes they could possibly do there that would keep early-game sailing / Exploring possible, etc. (NOT ramp up the danger of ocean too much).

My best guess would be a good solid 2 years , and probably a bit more until 1.0.