Depends. I normaly get one up just after I got my zerglings, queen and early spine crawlers up. There a cheep building and upgrades take ages to research.... So I like to start early
i always wonder the same thing. i've watched a lot of replays where they tend to do it after their first natural is put down.
Zerg: A good time to drop down an Evolution Chamber is around 50 supply. Terran: Around 40 to 50 supply. Protoss: Around 40 to 50 supply as well. It seems the 50 supply mark is a decent time to begin upgrades as that is when mid-game starts and economies (or expansions) start booming.
I like to throw them down sooner than 50 against protoss. If I scout an early stargate or lots of gas I make a few spore crawlers along the mineral line to protect from the void ray rush.
I like getting one to block my spine crawlers to prevent them form getting surrounded. Against terran, I put it near the bottom of my ramp. So I guess, I make an evo when I expand.
about evo placement... if you're going for ultra/ling, or roach/hydra or something that uses the same upgrades, get 2 evo chambers and put them in the front of your base as a partial wall off and put your spines behind it. You can upgrade twice as fast and they are fairly cheap buildings that release broodlings on death.
yes i have seen them used in pro games where they prevent the spine crawlers being surounded, the only thing is that you need to make sure not to let them get sniped before the upgrades finish or cancel them so that you don't lose as much when they're killed. If you can begin doing this now when you get to higher level play that could mean another unit or two witch (i'll bet rarly happens) but could help you win the game.
