Either view is acceptable in the PCA, whose short answer is, "We don't know." Its 28th General Assembly resolved as follows: That since historically in Reformed theology there has been a diversity of views of the creation days among highly resected theologicans, and, since the PCA has from its inception allowed a diversity, that the Assembly affirm that such diversity as covered in this report is acceptable as long as the full historicity of the creation account is accepted.

The detailed report of the Creation Study Committee discusses all the various views and their history and can be found here.

Blessings,
Clay