I can only agree with what others have already said on this. This is primarily a question of terminology. For us MLs what we usually mean when we speak of actually existing socialism is a state that is in the transitionary stage between capitalism and communism in which the society is being developed and guided toward communism under the dictatorship of the proletariat.

Building socialism or socialist construction are essentially ways of saying the same thing and i personally prefer using these terms because they emphasize the fact that this is an ongoing process, it is a movement towards something and not a static state. I like to say socialism is something you do, not something you are or have.

There is no timeline that says how long this process will or should last as that depends entirely on the material conditions of that specific society as well as on the external conditions in which that society exists (in the present global context limitations are imposed on the development of AES states toward communism by the dominance of neoliberalism and the threats of neocolonialism and imperialism).