I was toying with the same concept. I counted this morning several pit stops at Sepang. Average: 35 seconds. Number of pit stops averaged: 4. Clock used: an old Nina Ricci automatic mechanical clock...

The average official pit time for the four pit stops I clocked was 8.6 seconds (the time they show onscreen).
I started my chrono when the car took the turn into the pit lane and stopped when I judged that the car was as fast as the other running cars, in the curve after the pit exit.
The problem is I have no good data on lap times. How I miss Gale Force!
http://www.galeforcef1.com/. This means I find it difficult to calculate how much your lap times are affected by your fuel load. Besides, the estimates I have found on the actual quantity of fuel the cars have inboard vary wildly. But...
If you call Ta the time for an average lap with full fuel load, and you start with a full load (go, Kimi!), then the first lap takes Ta (duhhh...). If you call Dt the differential in time you get by one lap worth of fuel, next turn takes Ta-Dt, next turn Ta-2Dt, etc. This means that your time for the entire race would be N*(Ta - 1/2*Dt), if you could cover the N laps of the race with the full fuel load. The tires are acting against your times. Lets think this is a lineal effect: every turn you are slower by Tt, the time your degrading tires are adding to your lap time. So, your first lap takes Ta, your next lap takes Ta-Dt+Tt, etc. Finally, in a zero-pit stop strategy, your race takes N*(Ta-1/2*Dt + 1/2*Tt)
Actually, you can cover only N/2 laps, if you are on one-stop strategy, or N/3 if you are on a two-stop race, etc. After the N/2 laps, you expend Pt in pit time (the 35 seconds I measured).
On a one stop strategy, your total time would be N*(Ta-1/2*Dt+1/2*Tt) + Pt.
I am too busy to take this to its conclusion. If nobody is interested, I would retake this thing next week... Besides, I bet there is some kind of lap times calculator around the Web.
