The Ancient Mediterranean, from the beginning of time to the 1st century A.D.
Even though Ovid starts out by talking about the creation of the whole universe, for most of the poem his focus is more limited: on the Ancient Mediterranean world, including Greece, Rome, North Africa, and Asia (i.e., Asia Minor or Modern Turkey). There are a couple of reasons for this more limited scope. The first is pretty basic: the stories Ovid was retelling came from this region, so it made sense for him to set his poem there. The second is a bit more interesting: by referring to details his audience would be familiar with (including geographical details, local customs, words in common usage), Ovid could then surprise them by revealing the weird, sometimes mythological origins of those aspects of everyday life.