Why the time factor? I don't find it particularly matches my intuitions directly, and as pointed out it makes having children arbitrarily bad (which also doesn't match my intuitions). Say we give each person's death a particular negative utility - histories in which they die get that single penalty regardless of time (though other independent time factors might apply, such as the sadness of their loved ones). Does that fit any better or worse with your conception of death morality?

(Incidentally, I was thinking about this just a few hours ago. Interesting how reading the same comment can trigger similar lines of thought.)