Frank
So the pit stops are actually correctly matching the fuel load, except for that odd tenth of a second Paolo mentioned which is likely a result if tiny differences in remaining fuel in the car (also the remaining fuel in the report is at finish line, not the actual load at pits) but the time lost happens before/after the pit stop?
The in and out laps are a different matter. As Paolo wrote they are generally working much better but not completely without issue and certainly, as it should be, not always the same no matter what. There are self-inflicted things like running out of fuel, normal things like traffic effects (other cars totally shouldn't be just like air, a car just shouldn't, for no good reason, wait until the other car is 1 second+ away) and occasional issues like the known weird speed differences towards the end of /leaving pit lane.
I only used in and out laps to measure the time gap because I can't see the actual stop times, and the person I'm comparing it against I know used the same fuel and wasn't boosting. For the most recent race I was in, I lost roughly 1.25 seconds to someone in the pits, and they put in just 6 liters less. That's 2 laps at most tracks, and I've seen plenty of people put in 2 laps extra fuel and not be affected in the slightest in pit stop time. I came in ahead of this person and came out behind by a good margin, both time and position wise. The intention of code may be that the stops are based only on fuel, but that's not what actually happening on track.
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Frank Thomas 
Community Manager