Obviously depends on the size of the ship, and how familiar you are with the editor.
My 1st ship, which I don't even use, it was pretty much just to learn how to use the builder, took ~10 hours.
My 2nd and 3rd ships took ~8 hours.
I'd say it's a bit more complicated than space engineers, you have to take into account cabling and pipes, structural integrity, and the fact that you can only use set sizes and shapes of parts. Starbase ships can get a lot more detailed than SE ships, but obviously that means longer to build.
That being said, SE can handle much larger ships due to using blocks instead of voxels.