Na ordem de maior rapidez:
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Rede de floo :
Definitivamente, não instantâneo, mas muito rápido:
'But don't panic and get out too early, wait until you see Fred and George.' (CoS)
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Chave de portal :
Parece haver alguns segundos:
It happened immediately: Harry felt as though a hook just behind his navel had been suddenly jerked irresistibly forwards. His feet had left the ground; he could feel Ron and Hermione on either side of him, their shoulders banging into his; they were all speeding forwards in a howl of wind and swirling colour; his forefinger was stuck to the boot as though it was pulling him magnetically onwards and then –
His feet slammed into the ground; Ron staggered into him and he fell over; the Portkey hit the ground near his head with a heavy thud. (GoF) -
Aparição :
Isso parece ser o mais rápido subjetivamente, mas é claro, dada a proficiência geral da JKR Maths, ela não era tão precisa quanto se preferiria para comparações numéricas:
Harry felt Dumbledore's arm twist away from him and redoubled his grip; the next thing he knew, everything went black; he was being pressed very hard from all directions; he could not breathe, there were iron bands tightening around his chest; his eyeballs were being forced back into his head; his eardrums were being pushed deeper into his skull and then –
He gulped great lungfulls of cold night air and opened his streaming eyes.e
Twycross stepped forwards, turned gracefully on the spot with his arms outstretched and vanished in a swirl of robes, reappearing at the back of the Hall. 'Remember the three Ds,' he said, 'and try again... one – two – three –'
Além disso, há mais duas maneiras de viajar quase instantaneamente:
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Gabinete de desaparecimento. Nós não sabemos o quão rápido ele te transporta ou se está usando um dos 3 métodos acima (sem informação sobre o cânone), mas presumivelmente é tão rápido quanto os outros métodos.
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Como @Kushtrim P. observou em um comentário, você pode usar o tempo-turner + método de viagem normal (sua velocidade de viagem espacial pode ser tão lenta quanto você quiser, mas o tempo de chegada absoluto é arbitrariamente pequeno devido ao tempo deslocamento). Esse é realmente um método muito conhecido de viajar em ficção científica.