As all we can find out is how much data we've used for the month, and that's possibly a day out of date, does anyone know when that figure is updated?
Being updated at midnight would make sense but it doesn't seem to be then.
I don't know of a source that answers your question directly, but my impression is that it updates happen around the clock, and not at any particular time of day. Comcast says usage is added to the meter a few hours after it occurs, but may be delayed as much as 24. You might want to check http://www.netforecast.com/wp-content/uploads/2015/06/NFR5120_Fourth_Comcast_Meter_Accuracy_Validati... which is the most detailed description of the process I know of.
It was Comcast support who told me about it being once a day. I suppose writing something which scapes the web page regularly may be the best I can get.