Just to be clear. Working 4 hours or 1 series in a popper station IS WORKING. When we hosted a double Master and Junior along with a single Senior, we needed paid help for Master and tons of volunteer help for the rest. As Gun Captain I promised club volunteers that I would get them replaced after one series or less if they were running a dog. Most folks will avoid volunteering for a station because they normally get left out there for long hours in all kinds of weather. I had a better response when I promised replacements and held to my work. So working a station for 4 hours is HELP, and if everyone put just 4 hours in there would be less of a labor shortage.
Understanding the staffing needs for a hunt test is best appreciated if you have actually been the Gun Captain for a few tests.
There is one old training day rule that applies working at a hunt test, "throw more birds than you dog retrieves" or "if its not moving, pick it up and move it".
To answer you question about dropping a local test to help out, well I have done that to judge and we do not have enough locally just to skip out on one.