The first set to the hot springs took a few months (I think three or four, but I can look it up when I have more time) because Leon had to figure out how to set up the symbols. I believe Toph made the stone containers via earthbending, and then metal doors were attached, so actual construction didn't take very long.

The second set to the beach took several weeks because Sokka had to physically build the metal containers, then one of the containers was transported out to the fort.

Leon can set up the symbols pretty quickly. So Leon's really limited by how quickly someone can create the containers.