Twice. Once to power the device on, second to start the track recording, unless you enable Auto-Start, in which case you only need to turn on .power. If setup correctly, the device can automatically start recording your ride at whatever speed you tell it to recognize.

FWIW and judging by your tone in the posts, it sounds like you are searching for reasons to not like the GPS type units and that's all fine, a simpler Cateye or Sigma unit might give you less to complain about.