All night recordings NOT analyzed?

Note these key excerpts from Hill's book (pages 161 and 165):

I've already described how we used seven listening stations, each of which collected 24 hours of recordings.
...
Within a couple of weeks this team of part-time screeners was able to crank through about 72 hours of audio recordings per day. This rate of audio analysis was almost enough to keep up with what was coming in from the field, and if windy and rainy days were skipped, they could keep up.

Note that analyzing all 24 hours from each of 7 listening stations would require the team to "crank through" 168 hours of audio recordings per day; also note that quite a few of these "false positive" toots and taps might be produced at night.