It is all up to you. Honestly no offense to Notch in any way, shape, or form, but I don't believe that he planned out when Minecraft took place. To me its basically it's own world/timeline. Unless you think of survival as post apocalyptic which seems reasonable (so does the dimensional theory). The idea of a timeline is sort of irrelevant except to those of us that love a storyline .
When does Minecraft take place?