The 9-minute snooze is a product of mechanical clock engineering and digital clocks have followed suit since.

Mechanical clock engineers had to configure clock gears to work with the clock's other gears. They had two choices - to set the snooze for either a little more than nine minutes, or a little more than 10 minutes. Clock makers decided on the 9-minute gear, believing 10+ minutes would be too long and allow someone to fall into a deep sleep.

Clock manufacturers today have the option to set snooze buttons at any length but it is most stick with the 9-minute custom.