Who was the quickest from "unrated" to GM?

Question

What player attained the GM title in the shortest amount of time, beginning from their entry into organized (rated) chess, to the award of the title (either via attaining norms, or by direct award)? I would imagine that this player would probably also be in contention for "youngest to attain GM title", but I know this doesn't necessarily have to be the case.

(For purposes of this question, when I refer to "organized chess", I generally mean competition in an event rated and sanctioned by FIDE, or sanctioned by a national sanctioning body recognized by FIDE (whether that play is rated by FIDE or not)).

Answer 1

0 days.

There are 28 players who achieved the grandmaster title immediately:

 1            Fischer, Robert James                  
 2            Spassky, Boris V.                      
 3            Korchnoi, Viktor                        
 4            Larsen, Bent                           
 5            Petrosian, Tigran                      
 5=           Polugaevsky, Lev                        
 7            Portisch, Lajos                              
 7=         Botvinnik, Mikhail                      
 9            Smyslov, Vassily                       
 9=           Tal, Mikhail N.                         
11            Geller, Efim P.                        
11=           Keres, Paul                            
13            Hort, Vlastimil                         
13=           Stein, Leonid                           
15            Taimanov, Mark E.                       
15=           Gligoric, Svetozar
17            Huebner, Robert                        
17=           Bronstein, David I.                     
19            Gipslis, Aivars                         
20            Krogius, Nikolai V.                     
21            Panno, Oscar
22            Uhlmann, Wolfgang                     
23           Olafsson, Fridrik                                     
24            Balashov, Yuri S.                    
25            Savon, Vladimir A.                     
26            Vasiukov, Evgeni                       
27           Tukmakov, Vladimir B.                    
28           Boleslavsky, Isaak  

When FIDE first published their rating lists, these were the grandmasters who were deemed such by FIDE. Therefore, it took them zero days to become a grandmaster.

(Source: http://www.olimpbase.org/Elo/Elo196900e.html)

Answer 2

While various chess rating systems have been used since the 20th century, with the most impactful being the FIDE rating established in 1970, it seems to have no consequences for this question. This is because the list of "quickest to become GM" will indeed closely, if not entirely, coincide with the list of "youngest GMs".

One reason is that with people in the past it is often quite hard to ascertain when they started playing organized chess. Another reason is that requirements for the title of Grandmaster are arguably getting less hard over time and the practice of establishing GM tournaments with the aim of facilitating fulfillment of GM norms is not entirely uncommon.

Therefore the list of youngest grandmasters and list of grandmasters under 15 is the place to go, with maybe even Fischer in the "pre-GM-norm-hunt" era being among the candidates for primacy; nowadays children prodigies play competitive chess since as early as 7 or 8. Fischer joined the Manhattan Chess Club at the age of 12, although he played at least children's tournaments since 1952.

Answer 3

The youngest GM in history is Abimanyu Mishra at roughly 12 years of age. If we are counting age here is is the person. If there were not COVID there would have been OTB games and an even more likely chance to get a norm faster. He got his final two in the space of a couple of months.