The current definition of AcquisitionDuration is

Duration (in seconds) of volume acquisition. Corresponds to DICOM Tag 0018, 9073 Acquisition Duration. This field is mutually exclusive with "RepetitionTime".

The definition of DICOM tag 0018, 9073 is:

The time in seconds needed to run the prescribed pulse sequence.

They also helpfully provide a graphic to clarify the definition:

So this is the duration of the full scan, which only overlaps for single-volume acquisitions. Our definition more closely aligns with
FrameAcqusitionDuration 0018,9220:

The actual amount of time [in milliseconds] that was used to acquire data for this frame.

I propose the following (re)definitions:

AcquisitionDuration: Duration, in seconds, of scan acquisition, including all volumes for multi-volume scans. Corresponds to DICOM Tag 0018, 9073 Acquisition Duration.
FrameAcquisitionDuration: Duration, in seconds, of volume acquisition. Corresponds to DICOM Tag 0018,9220 Frame Acquisition Duration.

This change needs to be communicated somehow. While upstream tools are going to refer to DICOM, downstream tools may only refer to BIDS. Any suggestions for wording?