Where & When
Based solely on internal evidence, there is no way to date the setting of the story much more precisely than ‘the Stone Age’. This is a vast stretch of time, perhaps 99% of the whole of human history, depending on your definition. However, we know that the writer envisaged the date as 100,000 BC and that that was even the title used in some early BBC publicity in the days before the serials had onscreen titles. The geographical location is even vaguer, and, again based solely on the story as televised, we can’t even be confident it’s on Earth, since the DW universe has many alien races physically indistinguishable from humans. However, it’s clear that that’s not the intent, so “somewhere on Earth, approximately, 100,000 BC” it is.