Imagine an extraordinary alternate timeline
Thinking logically a scientist in a Barbaric world would have many more challenges than a scientist living in the world we exist in.
The main challenge would be energy. A lot of energy would be required to even attempt time travel let alone be successful at it.
Also the time to just devise a plan may take centuries before it could be finalized. And the development of time travel itself may take several millennia to accomplish.
In short it would no doubt take ions for a plan to reach a successful conclusion. The Scientists, or as they are called in “In Who’s Hands/Cause & Effect” “the smart ones” would certainly know this and know that they and most likely 100’s of future generations will pass on before their plan plays out but when desperate, angry and fearful whatever needs to be done must and will be done.