A couple of things...
One. I am more disturbed and creeped out by Hillary's statement than I am outraged. For many this is the "last straw." For me, that was weeks ago, so I'm not getting all frothed up over this. I suppose it's Clinton Outrage Fatigue.
Two. On the other hand, I'm not going to begrudge anybody for cranking up the outrage over the remarks because they were outrageous, and frankly something has to drive her out and it might as well be this. But, the one interpretation I am not really buying—and the one most people are most readily reaching for—is that she is using a hypothetical assassination as a reason to keep running.
That, to me, is clearly NOT what she said, and I don't know why anyone would try and put those words in her mouth. It just doesn't make sense. In nearly all cases, whenever anybody "drops out" of the race, they are technically "suspending" their campaign, for various fundraising and technical reasons. So the idea that she needs to keep her campaign active in case something happens to Obama is preposterous. If something happened it's not like the Dems would let McCain run unopposed...and HRC would be the most logical replacement candidate as the runner-up, whether she had "conceded" or not.
That said, I cannot fathom a possible reason or context to justify her mentioning the assassination of a Presidential candidate. Period. Certainly not to answer that particular timeline-related question, but not in any other circumstance I can think of.
That line becomes especially creepy when the race had basically reached the point where the discussion has turned to the possibility of her being the VP, and thus the first successor. One would think that invoking anything regarding assuming office due to unforeseen circumstances would be a topic given a very wide berth.
But when the likely nominee is a black man, Clinton should never have even gotten close to making a gaffe like this, because the very real shadow of Obama's assassination has loomed over the race as soon as he became viable—it's not talked about, but it's not necessarily far from people minds. And making it worse, Obama's not just a black man (as if that isn't enough) but a black man struggling to overcome the persistent rumor that he's a stealth Muslim raise the stakes even higher.
In conclusion, I think it speaks more to the unraveling of Clinton as a candidate and a demonstration of a disqualifying level of self-absorption and self-importance, and an empty void where a President needs discretion, tact and understanding. Casually referencing a tragic moment of one of the country's most disgraceful periods as a talking point to be (repeatedly) used regard to what it means to a huge swath of the country is just another example of (both) Clintons' delusions of grandeur and historical self-inflation and sense of entitlement.