QB Issue Resolution:

I’m not a tax guru, but I would go with your time zone. As long as you don’t count it in both years, I think you should be ok but consult with your accountant or tax pro.

Resolution for Issue 'Year-end purchases time zone differences' available: Yes (Solved).
Source: Intuit Community forum.

Year-end purchases time zone differences: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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