Hi,
Most RI's are from bacteria etc that are already present in the animal.
But if the animals immune system becomes weakened by stress/ incorrect husbandry or reasons we do not yet understand then the bacterial load can get to a high enough level to cause the animal problems.
I don't think leaving them for 4 days would be enough to set off an RI but changing the bedding to something that deals with it a little better sounds like a sensible precaution.
What do you use at the moment?
Also increasing the ventilation might not be a bad idea to dry them out faster?
dr del