setting for heart rates on workout

There is no setting as such,when you start a workout your watch measures your heart rate constantly and when you're not in a workout the watch checks your heart rate approx every 10 minutes.

There is a feature in the watch to notify you of a low heart rate or a high heart rate these are editable.

Heart rate notifications

And yes you can see your heart data in the health app on the phone.

There is no setting,the heart rate app measures your heart rate constantly during a workout and approx every 10 minutes when you're not.

Because you also have to travel the full 30 minutes at a brisk walking pace which is approx 3.3 mph.