The pieces I made yesterday are still drying, but I'll try to make a bunch more pieces today too. Takes about 24 hours to dry, or more if the air is a bit humid, to be completely dry, and you can't put paint and glue on them until they are completely dry, or the wet plaster can go soft and come off. While still damp, I can now see darker damp patches on the pieces, as it slowly begins to turn white. Also, they are really cold when you touch them. On some forums I was told that they are cold when they are still drying. So you can tell they are dry when they are completely white, and don't feel really cold anymore.
I sat some pieces up against each other to get an idea of what it would look like 'assembled'. This is my current idea for corridors. There's some more molds I haven't cast any pieces from yet, so that on occasional walls I can stick techy decorations like screens, fans, pipes, hatches and stuff to add some more variation.