(I know I'm replying to old comments, but I don't think this counts as a necro, so...) With regards to what time the isekai'd dudes came from, it's completely plausible for "god" to place these reincarnating people at different points along the space-time continuum than where they came from in the first place. Or, more likely, they're just randomly thrown into the space-time continuum and reincarnated into this world wherever and whenever because "god" seems to just make whatever mistakes when he kills them by accident and subsequently takes whatever actions to sort of balance out the karma.