Quanto tempo os elfos podem ficar sem dormir?

Elfos dormem, não apenas em O Hobbit, mas também em LoTR e em O Silmarillion , mas parece que eles podem passar sem muito mais tempo do que, por exemplo, anões . Quando Aragorn, Legolas e Gimli estavam perseguindo os orcs para resgatar Merry e Pippin sequestrados, Gimli teve que explicar a Legolas por que eles tinham que descansar:

And yet even I, Dwarf of many journeys, and not the least hardy of my folk, cannot run all the way to Isengard without any pause,’ said Gimli. ‘My heart burns me too, and I would have started sooner; but now I must rest a little to run the better. And if we rest, then the blind night is the time to do so.’

‘I said that it was a hard choice,’ said Aragorn. ‘How shall we end this debate?’

‘You are our guide,’ said Gimli, ‘and you are skilled in the chase. You shall choose.’

‘My heart bids me go on,’ said Legolas. ‘But we must hold together. I will follow your counsel.’~LoTR, The Two Towers

Quando Aragorn acorda depois, Legolas está acordado, de pé e reclamando de quanto tempo eles perderam.

À medida que a perseguição continua, os outros estão exaustos, mas Legolas está fresca como sempre:

For many hours they had marched without rest. They were going slowly now, and Gimli’s back was bent. Stone-hard are the Dwarves in labour or journey, but this endless chase began to tell on him, as all hope failed in his heart. Aragorn walked behind him, grim and silent, stooping now and again to scan some print or mark upon the ground. Only Legolas still stepped as lightly as ever, his feet hardly seeming to press the grass, leaving no footprints as he passed; but in the waybread of the Elves he found all the sustenance that he needed, and he could sleep, if sleep it could be called by Men, resting his mind in the strange paths of Elvish dreams, even as he walked open-eyed in the light of this world.

Parece que os elfos podem entrar em algum tipo de estado meditativo e 'descansar suas mentes' enquanto são fisicamente ativos, isto é, podem descansar sem deitar e dormir.

E na noite anterior eles conheceram os cavaleiros de Rohan:

The night grew ever colder. Aragorn and Gimli slept fitfully, and whenever they awoke they saw Legolas standing beside them, or walking to and fro, singing softly to himself in his own tongue, and as he sang the white stars opened in the hard black vault above. So the night passed.

Assim, parece que os elfos podem ficar acordados por um longo período de tempo com um pouco de meditação sem consequências. A questão é: quanto tempo eles podem fazer isso sem um sono 'adequado'? Eles podem fazer isso indefinidamente? Eles precisam dormir de alguma forma?