THIS IS A ROUGH DRAFT because I want to get up to date figures (where possible) and revise until we're as accurate as reasonable. I'm busy with a bunch of projects and will follow up later, but I have friends who may have the stats handy.

For the US as a whole, here's the arithmetic:
Half of households have at least one gun. Waiting period = worthless.
An unknown number can borrow one. We will table that, but keep it in mind.
Something like 80% of all violent crime takes place between midnight and 0500. (It has probably changed slightly since I first did this). There are no gun stores open during that time. Waiting period = irrelevant.
Only about .035% of people with guns ( larger subset than gun owners, since any convicted criminal may possess one, but doesn't legally own it) commit crimes with firearms.
So we're looking at the potential effect being on .000175% of the population. Statistically irrelevant.
Then there's the idiotic assumption that someone who is angry or insane to the point of lethality on Day 1 is stable by Day X and never has another issue. The number of people this would be true for is statistically zero.
And if someone DID find their partner in a cheating embrace, ran to the store, bought a gun, came back, found them both still there and shot them, there'd be a really good case for premeditation, not a crime of passion anyway.
Now, how many people with an actual threat from someone have been told a piece of paper will protect them, told to wait 10 days, and died before getting approval?