Ten thousand years from now (but 25 would do)
The modern icon of the flying saucer didn't actually penetrate our culture until 1947, when amid much confusion the term was publicized in relation to UFO sightings (the term UFO itself would take some more years to come by).
There were some examples and reports of discoidal flying objects before that seminal year, some even used the iconic expression. But there was no concept (much less mass sightings) of flying saucers as a kind of Universal design for alien spaceships. Flash Gordon and Buck Rogers used rockets. Alien Flying Saucers, that's a post-1947 cultural icon.
That's why depictions of discoidal aircrafts and spaceships before 1947 are of special interest. They are not that rare, actually, but each one of them should make you say wow.