Board Thread:The Panopticon/@comment-1783865-20181019214838/@comment-6032121-20181019220720

You're right that that's where the question lies, but it seems unlikely that the Stenza technology allows time-travel, or something of the sort would have been mentioned. (Considering what we've seen of their culture and their technology, if the Stenza had time-travel, they'd basically be on Dalek levels of dangerousness, and the Doctor would know about them surer than not.)

Considering that the episode went through the trouble of establishing that its "human" characters are not actually humans at all, it seems clear that the intention is that it takes place in the present-day of Series 11 Earth — notice how the humanoid-aliens in question haven't even heard of Earth or humans, suggesting this is before mankind starts taking to the stars and leaving their marks in "every solar system" as we know they did from Series 1 and countless other sources.

All that said, the above reasoning is, I think, the only straightforward, Occam-friendly conclusion, but it may still be too speculative for actual use on the Wiki. Let's wait and see.