If I recall right (and I can't find the article anymore, so it's probably hearsay), they had to start the lap from a different point to maximize the amount of electric boost they got from the hybrid system. Timing from the "regular" starting point meant they didn't have enough boost where it did the most good.
Fantastic car, but consider that it runs out of battery by the end of the first lap...
Then there's the McLaren P1, also a hybrid, and about 10 or more seconds faster than the Porsche.
Not that Nurb lap times mean anything.