Yes, 30 seconds is an arbitrary number. Many comparisons will be much faster, after much longer. And, no consideration is given to the collection of the images for comparison. But,the numbers a still good to think when consider what sorts of studies are feasible until a meaningful type of machine assist is developed or just the work involved in any individual project.
So for instance, I supervised a masters thesis that was a die study of 383 specimens. If the student had take a full 30 seconds on each comparison that would have been nearly 153 8-hour work days, nearly half a year. Not counting the write up. [The chart above using 24-hour days.] Obviously, on the republican series certain variations within a type, especially control marks when present, can speed up a die study, but even such sorting requires individual consideration and intense record keeping. Without such control marks limiting the number of comparisons required, De Ruyter’s 1996 study of the Coins of L. Julius Bursio would have required upwards of 5,287,700 unique comparisons (NC 156: 79-147).