Great points - a histogram might make more sense with the email volume graph and the labels for # of words can be improved for additional clarity. Thanks for the great feedback - please let us know if you have any more.
If you pull the data together it shows that the best way to get a response is to send a short message early in the morning (during his peek email hours): "the one time I reply to more email than I get is the 5am to 7am time frame."
Pretty good place to start if you want to get a response.