Quanto tempo demorou para que Palpatine viajasse de Coruscant para Mustafar?

Não há nada na Novelização Oficial do filme para indicar se o aviso que o Imperador sentiu foi em tempo real (nem nada para especificar a passagem do tempo entre receber o aviso e sua chegada a Mustafar), mas dado que Mustafar é descrito como sendo " uma colônia de mineração remota " no " Orla Exterior

Meu instinto é que o Imperador estava recebendo algum tipo de Force Premonition sobre seu aprendiz estar em perigo ao invés de sentir o lutar diretamente:

He didn’t have time to direct the search personally. The Force hummed a warning in his bones: Lord Vader was in danger. Mortal danger.

Clones scattered. He stopped one officer. “You. Call the shuttle dock and tell them I’m on my way. Have my ship warmed and ready.”

The officer saluted, and Palpatine, with vigor that surprised even himself, ran.

Também não há nada na Junior Novelisation do filme

Sidious knew he should have been pleased with the outcome of the fight. He had won, though it had been a near thing. But an uneasiness was growing within him, a sense of some threat not yet resolved.
Below, the clone commander boarded a Senate pod and rose to the level of the podium. “There is no sign of his body, sir,” he reported, saluting.
“Then he is not dead,” Mas Amedda replied.
Sidious nodded and reached out with the dark side, trying to sense where his enemy was hiding. As he did, the feeling of risk grew stronger, and he understood. Not a threat to him, but to his apprentice. He must see to this personally. “Double your search,” he told the clone commander, though he doubted they would find anything. He turned to Mas Amedda. “Tell Captain Kagi to prepare my shuttle for immediate takeoff. I sense Lord Vader is in danger.”
Mas Amedda bowed. “Yes, my Master.”

Desça a escala do cânon, o cânone do Legends Tokyopop! Star Wars: A Vingança do Cine-Manga Sith indica que a luta de Anakin com Obi-Wan estava acontecendo ao mesmo tempo que a luta de Palpatine com Yoda:

O filme Novelização gráfica é ainda mais conciso sobre o assunto

Quase instantaneamente (minutos, não horas) porque o ônibus partiu enquanto a luta ainda estava acontecendo e chegou Assim como Obi-Wan estava saindo com Padme logo após o lutar.

Chegada

At the landing deck, C-3PO stood on the skiff's landing ramp, waving frantically. "Master Kenobi! Please hurry!"
"Where's Padme?"
"Already inside, sir, but she is badly hurt." Obi-Wan ran up the ramp to the skiff's cockpit and fired the engines.

As the Chancellor's shuttle curved in toward the landing deck, the sleek mirror-finished skiff streaked for the stars. Obi-Wan never looked back.

Partida

Por favor, note que ele deixou durante a luta (que, no filme, durou apenas alguns minutos)

Clones scattered. He stopped one officer. "You. Call the shuttle dock and tell them I'm on my way. Have my ship warmed and ready."
The officer saluted, and Palpatine, with vigor that surprised even himself, ran.

e mais tarde, o texto mostra que a luta está em andamento depois que o Imperador pede o ônibus espacial:

With Anakin's grip on his wrists bending his arms near to breaking, forcing both their lightsabers down in a slow but unstoppable arc, Obi-Wan let go. Of everything. (all quotes from Chapter 20 of Stover's Episode III novelization)

Tempo após a luta até a chegada

E sabemos que o Obi-Wan correu da luta até o skiff, e baseado no filme não foi uma grande distância, já que levou apenas alguns minutos de intensa lutar para cobri-lo antes:

He would leave it to the will of the Force. He turned and walked away. After a moment, he began to run.
He began to run because he realized, if he was fast enough, there was one thing he still could do for Anakin. He still could do honor to the memory of the man he had loved, and to the vanished Order they both had served.
At the landing deck, C-3PO stood on the skiff's landing ramp, waving frantically. "Master Kenobi! Please hurry!"
"Where's Padme?"
"Already inside, sir, but she is badly hurt." Obi-Wan ran up the ramp to the skiff's cockpit and fired the engine