In terms of leaving it to a survey to see how long people wait at baggage carousels, surely the handling agents can, on request, supply the times from chocks on to first bags, or, is it only certain airlines/companies who record this for targets etc?
That way, its could provide a more accurate, and surely larger demographic, of waiting times (this survey size was a couple of thousand compared to the x million people who actually do fly per year).
For example, flight XYZ111 arrives at 1200 if Mrs Jones gets off the plane at 1205, then queues at immigration until 1235, and waits until 1245 for her bags, then she may only record for a 10 minute wait, whereas the bags actually took 45 minutes to arrive.
On the flipside Mr Bloggs gets off the plane at 1204, queues at immigration until 1215 but waits until 1245 at the same carousel as Mrs Jones, his bag wait time will be 30 minutes, so already there is a 'discrepancy'.
Therefore Chocks on (1200) until 1st bags (1245) is the more accurate measure.