Approximate Milling Times:
Brass: 30 minutes
Aluminum: 45 minutes
Stainless steel: 6 hours (with coolant) I had to try :)
I had one .0313" end mill to use for this project. The feed rates are conservative but reasonable. Feel free to experiment on your own.
When milling the steel, I used a little hot glue to form a wall. I much prefer to build a taller wall using modeling clay. (less mess!)
Cutting fluid used: