I saw that as well, but apparently the Times is not good on math.

They are recommending (correctly) that you do 5-6 intervals each session, 3 sessions a week.

You need 4 minutes between intervals and then a 20 - 30 second interval.  Let's assume 20 seconds, so if you do 6 intervals, 3 times a week, that would be 6 minutes of intervals a week, but you need to add in the 4 minutes between each interval (warmup, but no cool down, let suppose), then (4 minutes +  20 seconds) *  6 intervals * 3 days = 78 minutes of exercise, or about an hour 20 minutes, not 6.

I take a spin class in the winter, and you get the best results from that if you have an instructor that does intervals.  Unfortunately, most don't.

Bruce