Questions regarding historical/realistic torpedo settings

Hey there. Got two quick questions, both regarding torpedoes. I'm looking for actual historical/real answers.

With regards to impact and magnetic pistols, what was involved in changing from one to the other? How long did that take, and could that be performed once the torpedo was in it's tube (outer door closed and outer door open)?

With regards to setting running depth, what was involved to do that? Again, how long did that take to do, and could that be performed once the torpedo was in it's tube (outer door closed and outer door open)?

At the moment doing either is the work of a moment to click impact versus magnetic settings, and the same goes to changing running depth. For one, I'm honestly interested in learning how their torpedoes were fuzed and set, and for another I want to operate/play setting torpedoes realistically.

Any help or advice (or answers! :p ) will be greatly appreciated!