The placed-in-service date would be the date that you placed the vehicle into service, which would be on or after your purchase date.
Although the IRS hasn't released TY 2023 instructions for Form 8936, Clean Vehicle Credits reflecting this new part of the credit, this interpretation would be consistent with existing tax policy. Last year's Instructions for Form 8936 (01/2023) indicate simply that a taxpayer should "[u]se Form 8936 to figure your credit for qualified plug-in electric drive motor vehicles you placed in service during your tax year." [Emphasis mine.]
See the IRS' Used Clean Vehicle Credit for all qualification requirements.
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