I don't know answer to your question. But I suggest that the title of your post shall be clear. Since our forum is mechanical, there is no point to keep your subject "Mechaical"
When you know what the material is, simply Google, "estimating construction time for (pick one: Concrete, wood, steel, aluminum, Cargonite, clay, stone, paper, fabric, tin, Hastelloy, etc.) columns 3m length vertical".
Are you making it out of flat plate steel and is it being welded full pen ??? or is it made from rubber and being glued if it is made from metal and being made full pen i would estimate 12-16 hours