The maths associated with the elapsed time of a standing quarter mile shows you how much horse power you made available on that run at the rear wheels (poviding of course you have weighed your vehicle before hand including yourself).
We all know there is power loss through the transmission, and the biggest loss is down to tyres.
If you want to run with dodgy tyres then you will have a greater power loss, and of course, having an LSD will remove some of that loss. That's why we say it's all about getting the power down, it's no good having a shit ton of power if all you do is spin it away - how many times have you heard people say "yeah, my car spins the wheels in third gear mate" - whoopee effin' do, I'll be miles ahead while your smoking your tyres.
What we are after is a reasonable figure - something in which to demonstrate. So have a bit of practice first, get the hang of the starts and those sloppy gear changes. Weigh your car with half a tank of fuel so you have a reasonable average - maybe even take an average quarter mile time rather than that one off personal best.
How do you know that so-and so's rolling road is giving you an accurate figure, do rolling road fall under The Weights and Measures Act ?
I think not.