The durations are displayed in hours and fractions of hous as decimals instead of in hours and minutes. The reason is to allow for easier calculations when summing up the values in spreadsheets. So, in your example of 20 minutes, the fractional equivalent is .33 hours (20/60) and the 12.83 is the equivalent of 12 hours, 50 minutes. 50 minutes is equivalent to .83 hours (50/60).
You could certainly argue that it should be the other way around, but I have had people request it both ways. I had to pick one or the other at the time.