I turn it on every morning and leave it in tracking mode all day, turning it off when I stop for the night (or a little before if I am concerned about Spot stalkers). I can't imagine trying to remember to send an OK message every hour during the day.
Bob
I think Simon means the tracking interval when you have tracking on. You can configure the interval at which your track is updated on your spot configuration page to: 2 ½ (with Extreme Tracking only), 5, 10, 30, or 60 minutes.