When is a day not a day? That is the question.Do you have more insight?
Having just taken a look at this, it would appear that the problem occurs because one day is actually taken as the time between this update and the one that's about 24 hours ago. Because the clock doesn't start until the various files that are required for the update have been downloaded, there can be a variation of many minites. In the data currently displayed, the gap between updates was 24.04 hours.
You'd expect the score change to be 13555.303 - 1.347 = 13553.956
but adjusting for a day: 13553.956 * (24/24.04) = 13531.403 (which is what's displayed)
This adjusting for a day feature was designed for when the score update fails totally for a number of runs. When that happens it makes slightly more sense because the two comparison points will be much more than 24 hours appart.
Hope that helps.