Thanks for that, it clarifies misconceptions I had regarding the uncertainty possibly preventing a meaningful correlation between the emission and absorption of a single photon. It was claimed that such a correlation would be impossible to obtain (because of the uncertainty principle) when I argued (not on this forum) the merits of such an experiment in relation to a particular view of the single photon in flight in vacuum.

I have known that single photon generators are routinely used in experiments, but my understanding was, given current technology, that there is the possibility of such devices producing a sequence of single photons for each initiating trigger pulse.

So just to confirm my understanding:

Assuming we can trigger a laser to produce one photon per initiating trigger pulse, there will be a time uncertainty between the trigger signal and the actual generation of the wave packet. Upon detection, there will also be a time uncertainty between the absorption of the wave packet and the detected signal. In the example you gave, this would amount to a combined uncertainty of 20ns (10ns for emission and 10ns for absorption) which equates to a length of 7m.

If we were able to construct a vacuum chamber much longer than this 7m, with a laser accurately aimed at the detector, then there would be a small uncertainty in the time correlation between the trigger signal and the detected signal (the longer the chamber, the smaller the uncertainty). This would signify a valid measurement of single photon delay (subject to the uncertainty and taking into account known measurement delays) between the emission and absorption of a single photon that involved no interaction with any medium on route to the detector.