Have you realised this thread is over 2 years old...although still relevant. Better still, although paid service is the Sporttracks online site. Give it a trial.
the above site does this - I am new to it all really but I did notice it - and you can use garmin plug in to take all the data really easy - the website is busy looking with all the information but it is very good!
Ooops - I was looking a pace zone summary - the heart rate is a little less detailed!
Why can't Garmin add this feature in the 610? I need to know the amount of time I spend in different heart rate zones during intensity workouts. PowerTap does this for heart rate and for watts. Please work this one up for heart rates in the 610.