Hi!
There are around 60 levels (plus narrative scenes). The minimum playthrough time tends to be around 2 hours, but that can stretch to 4-6 hours based on your familiarity with puzzle games and if you want to see all the content.
Levels are built with one solution in mind, but the open mechanics lets you complete the levels in different ways (and I try to encourage that, I never block alternative solutions). On some levels, you can even reach the solution using fewer resources. So it's more open than your traditional puzzle game but not as open as a management game.
There's an old demo on Steam that I'll publish on itch if I find time to update it.