Jake is infested by a Yeerk, so his Animorph friends have to hold him captive for 3 days (9am on Saturday to 9am on Monday) until the Yeerk starves to death.
Meanwhile, Ax morphs Jake in order to cover for him. PP 151-152: According to his parents and his Controller brother Tom, "Jake" had been eating like he was trying to eat everything in the house. Tom says that last night (Sunday), Jake had eaten 6 pieces of chicken and an entire pie, and had kept yapping about how great the food was. Tom also says that "Jake" had kept saying things like "Potatoes. Toes. Tay-toes.".
IMHO, "Jake"'s weird behavior should make Tom suspicious as to whether he has any connection to "Andalite bandits". (Jake even wondered if Tom's new Yeerk was suspicious). He should then have shared his suspicions with Assistant Principal Chapman, leading to the early exposure of the Animorphs.