The answer is, as always, "it depends." Seriously , though- I time discount to an extent, and I don't want to stop totally. I prefer more happiness to less, and I don't want to stop. (I don't care about ending date, and I'm not sure why I would want to). If a trade off exists between starting date, quality, and duration of a good situation, I'll prefer one situation over the other based on my utility function. A better course of action would be to try and get more information about my utility function, rather than debating which value is more sacred than the rest.
...Which, of course, this post also accomplishes. On second thought, continue!
The first greatest good for the greatest number for the greatest number will start "first" (by whatever measurement is applied) but ends before the second greatest good ends and doesn't last as long (in total) as the third greatest good.
The second greatest good for the greatest number will start end "last" (by whatever measurement is applied), but does not last as long as the third greatest good (in total)and doesn't start as soon as the first greatest good.
The third greatest good for the greatest number lasts the longest (in total), but ends before the second greatest good ends and starts after the first greatest good starts.
What within utilitarianism allows for selecting between these three greatest good for the greatest number?