I've just finished and saved my race, and when I divided my time by 29 (warm up + 28 laps) to figure out my average, the maths didn't work. My average lap time was approx 2.0 seconds faster than my actual fastest lap time. Knowing this wasn't right, I double checked my replay (yup the whole thing, albeit fast forwarded). Sure enough I stopped just after the finish line at the start of the 29th lap.
Some ensuing investigating reveals that if you quit the race during your first lap (your warm up lap + your first timed lap, while the race says lap 1) the replay time will be for that time. But if you quit after you complete your warm up lap and 1st lap (so the race screen now says lap2) your replay time will only show the time of your first timed lap and nothing extra.
Eg, your warm up lap takes 1:40.000 (you time it manually) and then your 1st timed lap is 1:30.000, you then quit 20.000 seconds into your second lap. The total time is 3:00.000, but check your replay time, it will say 1:30.000. (When I divide my total race time by 28 it is pretty much what I thought my average time would be.)
This means that your replay is for the 28 timed laps only (nothing before or after), meaning you can take as long as you want on the first lap, and it also means you don't have to exit the race at exactly the start of the 29th lap, you can quit at any time during the 29th lap it won't affect the overall time the replay shows.
If someone else could verify all that, I'd appreciate it. It may prove to be useful info moving forwards.
Also, time submitted, It was a fun race featuring; Only 1 very minor bit of AI contact, A couple of minor offs & 1 big tank-slapper/spin exiting the final corner, apart from that completely clean.