Note, the information comes from the CIA IG report which, in the case of Abu Zubaydah, is based on having viewed the torture tapes as well as other materials. So this is presumably a number that was once backed up by video evidence.
The same OLC memo passage explains how the CIA might manage to waterboard these men so many times in one month each (though even with these chilling numbers, the CIA's math doesn't add up).
So: two two-hour sessions a day, with six applications of the waterboard each = 12 applications in a day. Though to get up to the permitted 12 minutes of waterboarding in a day (with each use of the waterboard limited to 40 seconds), you'd need 18 applications in a day. Assuming you use the larger 18 applications in one 24-hour period, and do 18 applications on five days within a month, you've waterboarded 90 times--still just half of what they did to KSM.
The reason the Bush administration used torture was to complete the legend of 9/11. They needed to create culprits where there were none...or at least in placed other than their own administration.