I bought Grand Theft Auto Vice City for my Mac and it gave me an activation key to activate before the game can begin installation. I did this about an hour ago and I wanted to know approximately how long does it usually take for the activation key to activate?
You key should have activated instantly and therefore your unlocked game should be inside your Steam Library. If it isn't check your steam inventory since it may have been put there by accident. The game should be available to download inside your steam library and it will install inside the SteamApps folder:
C:\Program Files (x86)\Steam\SteamApps\common\GTA: Vice City (64 bit) or
C:\Program Files\Steam\SteamApps\common\GTA: Vice City (32 bit).
The first time you run the game it will install any dependencies.
Once you enter the key the game should be added to your Steam library immediately. The dialogue you entered the key should have given you the option to install the game. If you missed that or chose not to install the game then you can install it by selecting the game in your library and clicking the blue install button.
When you put an activation code in Steam, it's automatic and at the moment.
If the code is not correct os "has some problem" Steam advertise you what problem is. If not, the next steps are few questions to install (or leave it for later) the game.
If the game is bought in steam, is automatic too, and don't need any type of code.
Activation is instant and you should get a window asking if you want to install the game at the same time.
If no window appeared and the game is not in your library then you can try adding the key again.
It is possible that there were network issues at the time you added it and nothing actually happened.
If you try to add the key again and it says it is in use but not in your library then you will need to contact Steam support or your vendor.