Seems that you have to wait for about a day before they will send you another mail with activation code and a link where you can use it.
At least this is what happened to me
So I've got a email that I won 1 month. Installed the game. Trying to login. It says that I need game time to login! I wasted 25 mins of my cloud gaming time installing the game and still can't play. So where is my free game time?