The right to claim and the amount of tax credit you can claim is based on the date on which you acquired the vehicle,where acquired means that title has passed to you under your state law. That's likely to mean that it's based on the date the title was issued. (IANAL).So, I shouldn't want to take delivery just before the end of a quarter after which it will drop, because there will be a lag between delivery and the title being issued.
Still a good idea to start away from dates on the end of change quarters. However, the state's actions are not a concern to the IRS.
Per previous IRS rulings, if you drive it, it's in service.
From Electric Vehicle Not Placed In Service by Year End, Credit Denied
Although "placed in service" is not explicitly defined for purposes of section 30D, other sections of the Code provide guidance. Section 38(a) provides a business credit against tax with respect to property in the first taxable year in which qualified property is placed in service by the taxpayer. See also sec. 1.46-3(d)(4)(i), Income Tax Regs. Property will be considered placed in service when it is in a condition or state of readiness and availability for a specifically assigned function. Id. subpara. (1)(ii); see also Consumers Power Co. v. Commissioner, 89 T.C. 710 (1987) (referring to investment credit for purposes of section 38(a)). [Trout v. Commissioner]