'Hourly 4-second sprints' is actually 5 times an hour 4 secs (bicycle) sprints. So it is more precisely about every 12 minutes. I do not understand why it says 'hourly'? Because it sounds less often?
That's how exercise usually works, and the study is concerned with the "least amount of exercise that can acutely improve fat metabolism and other aspects of health". Activity spaced out every 12 minutes would be disruptive and defeat that purpose.
I assume then each 4-s workout is followed by a 45-s rest. So 49-s * 5 = 245-s (4 min) spend each hour on the excercises.
You only need to rest four times!