You have to consider the reasons that people don't commit crimes.
For example, people (on the whole) don't shoplift because if they get caught they'll be arrested. That's all very well, but would they be more likely to shoplift if the consequences of getting caught was that the store's security guard would take you out back and batter you with a pipe? So would there be a rash of shoplifting, if the stores remained open but well-staffed? Quite possibly not.
On the other hand, the police (on the whole) don't conduct illegal searches because the case will be thrown out and they might be disciplined. If they had 12 hours with no law then you can bet they'd want to spend the time busting down the doors of drug dealers and mob lawyers, taking everything they can get their hands on that could possibly be evidence, questioning the bad guys and their immediate family members rather more aggressively than is usually allowed, perhaps destroying exculpatory evidence in existing cases. Some lawyers might betray certain clients, where their professional responsibilities to them have been onerous (but then, if the law doesn't apply does that necessarily mean you won't later be disciplined by a quasi-authority like a bar association?). Perhaps bailiffs would be collecting debts in ways the law wouldn't permit (although that's a tricky one: if you're going to do that why not forget about debt collection and just take stuff?). Landlords would evict undesirable tenants by force, that kind of thing. The press would break every court injunction and (assuming civil as well as criminal law is suspended) take libel risks they normally can't. Chemical plants would dump a year's worth of toxic waste in the river, assuming they can store that much. Want to pay someone a bribe? Do it tonight. The people most likely to be out smashing windows are glaziers.
In some cases your condition is ambiguous. If I fire someone on this night because of their membership of a protected class, then the following morning are they actually fired, or can they still bring action against me on the basis that their being fired is a continuing act and not a single action restricted to the 12-hour period? Similarly, can I just declare this night that a contract I've signed is no longer valid and be done with it, or will it be right back in force the next morning? The economic consequences of it being in general legally impossible to commit yourself to a contract that lasts beyond the next special night would be really profound (no long-term loans, for a start), far more than those of a few murders and broken windows, but I'm not sure whether you expect that to be the case.
Can my bank just keep all my money by zeroing my account that night? If so then the economic consequence is that banks are no longer considered safe places to keep money: the resulting cash/barter economy will last all year round since you can't in practice take all your money out the day before and put it back the day after. Or does the bank have a contract with me that will be enforced any other time of year to ensure they can't do that regardless of what silly games they play with numbers in their computer on the night itself? The nature of the suspension of normal law matters.
Murder is a crime that, for those few who want to commit it, the law is a major restraint. It's easy to kill someone and difficult to get away with it, so if you don't have to get away with it then those with murderous grudges will like their chances far more on this day than any other. For example you might see a lot of people who have been acquitted of crimes or charges dropped in the past year, targeted by their victims (or, even if they genuinely were innocent, by vigilantes). On the other hand, the kind of person who might shoot up a school (a) isn't that fussed about being arrested and (b) will do it when the school is open, not at night, so won't be affected.
You also have a social signal that "the rules" aren't in force, which sometimes happens in the real world when the police lose control of a situation. As such, rioting, looting and general destruction might increase. But in a "normal" riot, those who wish to defend their property still feel restrained by the law even when the rioters don't. In this situation, you might not just smash the window of a McDonald's restaurant to stick one in the eye of global capitalism (or whatever reason) if you know there's a guy in the restaurant who's been hired to shoot you if you do.
Personally I'm not sure much would happen outside of certain socially-agreed "hotspots" where trouble would concentrate. After all, if someone wanted to throw a brick through my window tonight and run away, then there's very little chance they'd be caught. So why would they be any more likely to do it on the special day? The people who want a rumble would all congregate in the town centre, or in a park somewhere. My windows would be pretty safe.
As such, I don't think the economic consequences would be catastrophic, except from organisations capable of committing truly massive crimes (like the toxic waste I mentioned above). Note also that even if there's no legal repercussions, there would be social ones, and so many people would still feel constrained by an approximation of the law. The news the next day would be all-over pictures of people up to no good: if they smash up a shop they'll be barred from shops in retaliation, maybe fired from their jobs, and since the matter isn't sub judice there's nothing to restrain the press from reporting their names. So you might even find that the streets are almost empty that night, and that simply being out marks you as a horrible person to be shunned. There's no better time to murder your spouse, so people who don't trust those they live with are going to have a nervous time of it, but that's not an economic consequence.
Final thought: I would really, really not want to be on the roads anyway. Someone who wouldn't even dream of punching you in the face would run a red light through a pedestrian crossing given half a chance.
