It's a shame there is so much false info out there and cowboys. Go on FB and peoples names get branded about as being great, yet go on forums (that have been around waaaay longer than FB) and you find those names don't dare post on them anymore as they have been shown to be cowboys.
Few key things for mapping,
1. Dyno maps should always be road tested after being finished. Dyno's are good tuning/diagnostic tools but arn't 100% road simulation
2. Faults can not be mapper round. Sensors are a common one that fail, if one has dropped, it needs to be repalced prior to mapping.
3. It's not all about power. This is for two reasons, 1 the harder you push it, the more likley to fail it is, 2 drive ability will make more difference to have it performs than 5 or 10 extra BHP
4. A decent map takes time, if they claim to be done within 30 mins its highly likley they have rushed it (although i do know very very rare occasions this isn't the case), so if its a 'mapping day' it's doubtful they will take the proper time to map it because doing a proper map can, if things dont go easy, take several hours or more.
Slight explanation for the caveat point 4 (ok long explanation haha).
Experienced mappers typically start with a base file they apply to the car and then tweak it to suit..
Mappers will see hundreds of cars over a year, say they do only 2 cars a week, that's 104 cars. if they map for 10 years thats 1040 maps they have in their library. So if you take an example of an 2005 sti, with decat, panel fiter and fuel pump (pretty much the starting point of modding) the experienced mapper will prob have 20-50 maps of exactly the same spec car and mods. So they will have a good library of base maps to start from.
base maps typically have lower boost, less timing advance and more fuel than the final map (much safer but lower performing map). Those are the perimeters that the mapper can adjust to improve the map for different cars. Or the mapper may take a conservative map he's done before and use that.
So you might be saying, the mods are the same so the alterations must be the same for a car with the same setup. The bad news is that isn't the case and that comes from personal experience and im not even a mapper.
I used to have a 1999 UK turbo, i ended up having a stand alone autronics ecu fitted to it, so the standard ecu was remove and autronics unit fitted. I sold that ecu to a mate for his car that was same year, very similar milage, same model and same mods (decat and panel filter at the time iirc). Knowing the maps may be out it was swapped at a rolling road day and the car went straight onto the dyno for a check. The run ended up being terminated halfway through the first pull, it was lean, timing was off and it was detting. The ecu was removed and refitted later just before it was mapped (due to a license on the ecu).
So now i've waffled on about what seems irrelevant to why very occasionally cars can be mapped in minutes here's the answer, very very occasionally a map is applied and it just works. If the mapper tries to add more timing, the engine dets, he adds fuel, it dets, adds more boost it dets. So the map that gets applied is as good as its gonna get for that car at that stage.
But as said this is very very rare the map applied is that spot on..