The 48 to 72 hrs for ketosis to begin is for water fasting. With the MC since you are consuming carbs "actual" ketosis will vary greatly depending on the individuals metabolism. Some folks with very slow metabolism as is the case with most obese folks might never actually go into full ketosis on the MC but will still loose some fat from the cleansing action of the MC and the inherent fact that most toxins are stored in fat.
Since fat loss on the MC is only a "by product" of the Master *CLEANSE* the whole issue with fiber (pulp) is not whether or not one goes off Ketosis it is the *fact* that the body has to produce hydrochloric acid to digest fiber thus changing the actual chemistry in your digestive tract and counteracting the alkalizing action of the lemon thus unequivocally changing and interfering with with how the MC was designed to work. Add to this that the fiber requires peritalsis to move it out which also works at odd with the MCs main MO of giving the digestive system a rest.