I’ve often thought that if time travel were possible (let’s say fictionally possible rather than scientifically possible) it would basically mean that it *always* exists once it’s invented.
It may be that much like certain areas in space have big cities that there are certain years that are more accessible. Like, maybe being in 1973 with a broken time machine is like being stranded in a small town with no bus and you have to walk to a city. Perhaps you’d have to live a day-to-day life until 1978 when someone else shows up. I suspect there would be a sort of “friends of time travelers” society, like a AAA service.
The temptation (in a fictional world where time travel works, regardless of whether it’s physically possible in our world) would be to not just observe the world, but actually write/direct/edit it.
The fun part is that if this were possible, the idea of this “messing up the natural flow of time” is impossible from our perspective, as we would have been born into this system.
If you’re looking for evidence of time travelers, societies that have deep historical roots might be an interesting take. Look for the organization that could pass a message along for a few centuries, or societies whose traditions and styles of dress remain static so that a stranger amongst them wouldn’t stand out to initiates.
With this in mind, here are some likely candidates:
1) Monks of all sorts.
2) The Amish
Can you think of others?
Also, of course, Halloween is a great time of year for this, which is what got me thinking of it in the first place.