This is interesting analysis, but it's based on NYC MTA countdown clock data which is just rampantly inaccurate on lines other than the L. It is regularly, customarily, up to 4 minutes off in either direction, in my experience.
Since trains are supposed to be spaced out 4-5 min or so, that means the clock is only really useful to tell if there's a huge delay.
Since trains are supposed to be spaced out 4-5 min or so, that means the clock is only really useful to tell if there's a huge delay.