mh, don't know if they calculate fee in the 'last second' or if they use a average of the day.
but yea, guess you are right.
I guess it comes down to it we really can't know for sure what GM does or when they do it...it's that whole transparency thing. If someone like me decides to throw together some sort of relational chart for a visual, there are only a couple of knowns. The rest is guess work. I think the charts do a pretty good job of relating Payouts, BTC Prices, and Difficulty in an easy to visulize way. I know it helped me to get my head around what was going on.