Now *this guy* knows how to make a protest sign.

[Spike89]

25. We're not communicating somehow

I'm maintaining that under the conditions you've laid out, time travel can only exist if it already exists. Let me try once more to clarify my position.
Say time travel is first discovered 200 years from now (I'm dead). The discoverer travels back 200 years in time to "now". Once here, the traveller tells someone how it works--at that point, time travel is discovered in my lifetime. Because time travel now exists in 2012, I go back to 1776 to talk to Thomas Jefferson and show him how to build a time machine. Time travel now exists throughout the entire history of the United States.
In other words, time travel is akin to a highly contagious virus and once it exists in any time, it exists in every time.
So, they don't have to come back specifically for me.