In Garmin Connect/Garmin Connect Mobile there is a setting that allows you to turn on/off the feature. It is under the device activity tracking settings in GC/GCM.
My apologies, I was thinking of the Forerunner 35 which has a setting to turn on/off the Move IQ feature. The Move IQ feature in the Forerunner 30 is always on by default and is used to help categorize activities after the timer has started since it doesn't have separate activity profiles. So there isn't a setting to be turned on and off.
Since this is the case we would recommend that you start the timer your walking and running sessions to ensure that all activity data is captured.