If they had seen a G35 before and tuned it with Haltech, assuming they had similar mods to you, then they would be able to tune it quickly. Will also benefit others who do the same as you now, as they have your map as a base, so anyone going with similar mods might get it done even quicker
Not a pro in this area but heard you cannot really use maps between cars anyway since there will be certain difference that can't be accounted for? Pingu, do you have access to the ecu or is it locked down?
(sorry ment to say not 100% exchangable...)
No idea in this car, but on my old Leon, you used to be able to get different "Stage" tunes for the mods you had of a place called Revo Technic (something like that). They had generic maps that could be used on the car depending on what mods it had. Obviously it wont give you the most gains as they have to leave a decent level of overhead in there, but it certainly worked.
In Pingus map, I'm not saying they could apply it to my car and off I go. It just means they dont have to start from scratch again so saves time. I.e. might take just 2hrs to tune rather than 3hrs+. At the end of the day, tuning is all about getting to know the ECU and the engine, so the more they see, the quicker they will get to a certain point