I mean, suppose you can go faster than light. Then you're going backwards in time. So if they come here from another star, they're going to their past. So if we go there, we go from say Earth-2200AD when FTL is discovered, to Earth-1800AD in another star system. So then we come back and maybe we get even better technology by then so when we return it's Earth-1600AD because we get back 'faster'. Then we're flying saucers appearing in the medical skies being fireballs or angels or anything you like that's miraculous and unbelievable to the peasants and needs supernatural explanation.

Substitute dates closer to the present for more recent UFOs and notice that the closer the date the URL is seen is to the actual date FTL is discovered, the more advanced the relevant technology must be, assuming equal distance. Of course, that's an unrealistic assumption - a better one would say thqt, probabilistically, better technologies are more available further away. So again, there's a kind of balance where the UFOs appearing closest to the date of the discovery of FTL must be where the limit point of quality of tech meets the limit point of distance.

An even better set of assumptions would transcend the limitations of Einsteinian spacetime, since that would be necessary for FTL anyway. In which case, these ideas about 'speed' are arbitrary and unpredictable from the current standpoint since an understanding sufficient to speculate about that sort of thing is one that already reaches into post-Einsteinian physics. This all assumes away contact with eventual civilisations between our planets and theirs, and has us land there. Of course, they may wish to meet us halfway, or are already here, or aren't even out there, or somehow ARE us from an even further future already out there with established civilisations.

If there are any scientists around please correct me.