I believe they changed the price feed from 7 days to 3.5 days back when they changed the amount of time it takes to convert Steem Dollars into Steem.
I don't think the estimated account value factors in the market price for Steem Dollars. I think it counts each Steem Dollar as $1.00, regardless of the current price.
I could be wrong on either of these points, but I'm about 80% sure they're correct.