If I may add some detail to that wonderful graph, please note how the raw times (jagged line) vary around the mean (smooth curve). As time goes on, this variation lessens as the subject gets more practice, which is exactly what is shown. This phenomena is not unique to Bansai. Anybody will show the same pattern given enough experience.
I will never set a record unless I get first crack at a brand new puzzle (Stephen?), but I privately celebrate if I come within 30 seconds of the record.