I feel like a fair number of people would find themselves able to rationalise it as not being actual murder.
I mean it clearly is murder, it’s just that pressing a button on a box seems so distant from other acts of murderous violence, I think a lot of people would press the button.
Maybe they would feel guilty about it after the act but not enough reluctance beforehand.
You are not going to get advance notice allowing enough time to pass any laws.
There’s now way that can happen in time. A significant percent of the boxes would be used in the first few minutes.
You have the 48 hours right? So aren’t going to save the first choice (which is a lot of people, assuming you can’t decide to un-press your button once the law passes, but before the 48 hours is up. You will have no way of knowing if you are the first person to choose your particular victim and hence liable for a first degree murder charge) but by the time people consider who their second choice is the button raids will have already started. I think that will discourage most people from pressing a second time.
It could create a perverse incentive to go out and kill your target the old fashioned way so that your button is still lit when the fuzz comes calling.
Maybe but only in the case where it’s your neighbor Jim who slept with your wife, not some huge well known politician or celebrity. For all the Trump, Obama, Putin, button pressers (which is going to be the vast majority IMO) is that’s not an option (or at least the risk of going out and try to kill them is much greater than the risk that you are the first person to say their name)
How would someone identify the person they were going to use the Black Box to off?
Do they have to use their name? Their full, legal name? Their online username? (Remember, I have the highest opinion of everyone on this message board…)
The box makes no mistakes. It will kill the person you are thinking of, when you decide they are the one.
As said its only the subsequent button presses you are trying to prevent (assuming there is a ‘no backsies” rule). There will be so many duplicate button presses (I’d be surprised if the numbers for Trump alone come in at much under a billion) it’s the 2nd, 3rd, etc. presses that turn this from a unprecedented catastrophe to an existential threat to society.
Also those laws will get passed SO FAST with a level of bipartisanship we’ve never seen. Everyone will be completely aware it’s the people passing the laws whose names are being called by the button pressers 
If you are say junior senator from Rhode Island, you might stand a chance of surviving the first press, but not 2nd, 3rd, etc.
They’d definitely be motivated. How do you know the difference between a box used prior to the law being passed to one used after?
No law gets passed that fast…especially when others could stop you with the press of a button. Getting all the countries to agree to such a thing, then actually enforcing it effectively before the shit hits the Final Fan? The amount of people refusing to sign on to this out of fear of being targeted will be quite high, I’m afraid.
48 hour limit, then all lights go out.
You wouldn’t, no grandfathering in. Being in possession of an unlit box==murder charge.
Possession of an unlit box after 48 hours just means you have a box…but so does everybody, and trying to arrest somebody for having an unlit box before the 48 hours is up means that Those Who Pass Laws did so before the 48 hours were up, and that enforcement of such a law was set up and running within 48 hours, and that those who get told that they have to enforce such a law hadn’t already used the box themselves.
Also, there are those magic words: “Come back with a search warrant.” 
With your finger hovering over the button
Ah I misread the OP I thought it would take 48 hours
There would of course be a thousand and one constitutional issues with the law but that doesn’t matter. Whether anyone ever actually gets sent to prison is irrelevant it’s just about making people think there will be reprucussions for the button pressers
I think the idea that passing such a law could make you a target would prevent such a law from being passed.
But the people passing the laws are already targets and know that. The issue is that without the 48 delay enough lawmakers will be dead to stop any laws being passed