On the episode when Vegeta and Trunks are about to go into the hyperbolic time chamber, Mr. Popo says that only two people can enter at a time. Then in the Buu saga when kid Trunks and Goten are training in the chamber, Piccolo and Majin Buu enter the chamber too. This means that four people are in the chamber, not two! So how many can really enter at a time?