"Placed in service" means that the car was delivered to you - not just on order. It must be a new, not used car.
The federal tax credit drops from $7500 to $3750 on April 1, 2019 for all Chevrolets. On October 1, 2019, the federal tax credit will drop to $1875. On April 1, 2020, the credit will disappear - unless Congress extends it. There is a bill in the House sponsored entirely by Democrats to extend the credit to all manufacturers for 10 years regardless of how many they sell. There is a bill in the Senate sponsored by a Republican Senator from Wyoming to immediately cancel the credit. Who will win? The President has hinted he would veto any extension. The House is unlikely to cancel the existing credit.
The tax must be used in the tax year you bought the car in. It cannot be carried over to a subsequent year. Thus, if you buy the car in 2019, you must claim it in your 2019 taxes and have enough tax liability to use it. So, for example, if your federal tax owed was only $6000, you only get $6000 in credit. They will not pay you for any excess. I made sure I had enough liability by taking out some money from an IRA I inherited. The good thing is that they will apply the credit against the liability first - before any withholding or other tax credits - like rooftop solar. For me, I'll get a refund of my entire withholding, plus a large credit for next year because the solar credit can be carried into the next year.
In Colorado, the tax credit was $5000 in 2018 and I believe it is still $5000 in 2019. That law expires in 2020, but a new law is likely to pass (since the Democrats control both houses and the governor - and he owns a Leaf and is pro-EV*) that will extend the law into future years with a decreasing credit each year for the next 5 years. (I think the bill drops the credit by $1000 each year.) Like the federal, you have to claim the credit in the tax year you bought the car. Unlike the federal, you have to prove you bought the car and registered it Colorado. (You don't have to buy it in Colorado, just register it. I bought mine in OK since none were available in CO at the time.) Unlike the federal, you get the tax credit regardless of your tax liability. I didn't have $5000 in Colorado tax liability, so they will send me a check with the difference as a refund! On the down side, I stopped withholding Colorado taxes when I bought the Bolt, knowing I would have more credits than tax liability. Colorado didn't see it that way and charged me a tax penalty for not paying enough tax through the year as the credit wasn't applied until after the year was over.
*I should add that there is at least one Republican senator in Colorado who owns a Tesla and is very pro-EV. You only get to sponsor two bills per year per senator and he is sponsoring two EV bills this year: "Don't be a gashole!" which fines you for parking in a charging spot without charging; and a bill to allow electric utilities to own and operate charging stations - which current law forbids. I don't know if either bill will make it through - the legislative session ends May 3 and the Republicans are stalling all bills to keep a red-flag gun control bill and an oil & gas regulation bill from being passed.
