It’s five days because Cecelyne is the Endless Desert. This means that it’s not exactly pleasant to cross. This means any army that wants to invade Creation from Malfeas, or vice versa, needs to be able to survive five days crossing the harshest possible environment short of Adorjan’s bedroom. It’s five days because even an army of demons marching across it is going to lose a significant amount of its number. It’s five days because it’s supposed to be Safely Removed. Further, it only leads to the most desolate and uninhabited parts of Creation. It is five days because, ultimately, Malfeas is irrelevant.
The Underworld and the Wyld are the Creeping Dooms of Exalted. They are the potential world-ending threats. The purpose of Malfeas, and everything inside of it, is not to be Sealed Evil In A Can. They are conquered and crippled and locked away, safely at least five days from even the most useless beachhead in Creation. The Primordials are never busting out. The demon hordes are never marching. You’re not going to see ‘portals to hell’ opening in Nexus or Meru.
Maybe an Abyssal can turn the basement of the house of ill repute she is running into an abattoir and start sneaking in armies of ghosts and zombies beyond the city walls to unleash in her clever scheme to topple the nation. But an Infernal who creates such a location is going to, at best, open a hole to Cecelyne and then it will take five days to walk across the desert to Malfeas and fetch her demonic hordes and another five days to walk back, and in that ten days some Sidereal may have noticed the problem, stopped by and done a few sutras and left the Infernal walking back only to find out her hole is gone now.
It’s five days because Malfeas is meant to be inconvenient. It’s five days and not a specific distance because it doesn’t matter how fast you move. You could shamble along at one yard a minute or run as fast as the rays of the Unconquered Sun himself, it takes five days so that you think to yourself “If I go to Malfeas to attend to my demonic armies, that’s at least ten days where my Creation-side plans will have to be left to the oversight of lesser minions. And I know that the Sidereals and Lunars have been snooping around. Can I risk leaving my beachhead without my presence for so long? But if I don’t go to Malfeas, then it’s possible the Quarter Prince will launch that attack on my barracks of trained blood apes!”
It’s five days to force players to make difficult choices. It’s five days to emphasize how much of a disadvantage the Yozi have. It’s five days to play into the themes of separation and division that Malfeas is supposed to embody. It’s five days because its cool.