I would expect that most people set their alarms in 5-minute increments, and dial in what minute they choose to meet the needs of their commute and morning rout

I would expect that most people set their alarms in 5-minute increments, and dial in what minute they choose to meet the needs of their commute and morning routine. This forces variations away from a "sharp" time spike. Also, alarm clocks are almost never right on time; I would expect that most alarm clocks are more than a minute off. This factor would smooth out the 5 minute steps I'd expect to see in the data. The alarm clock inaccuracy may decrease over time as people move to using their smartphone to replace yet another device.