Do such conflicts among the Extraterrestrial Alliance magnify the difficulty of obtaining a suitable degree of perfection in timing what they want to see happen when they time travel?

The need for this coordination and consent does greatly complicate things. It slows things down and it leads to errors because it, in effect, will force a more conservative, reduced scheduling of such endeavors because there will need to be a compelling reason and a well-thought-out plan that will be agreeable to all the parties. As a consequence, there are fewer than ideal repetitions for the purpose of having a do-over. So by default, in having some limit on how much fiddling and fussing they can do, it will be harder to refine any given circumstance beyond a certain level of perfection, so the interlopers have learned, many times, to be content with getting close in their objectives.