When the analysts are told to prove that the memos are true, instead of being told to see if the memos could be false, it does take hours to rationalize all the problems with the memos away.
Which is why we saw the subsequent ludicrous claim by CBS that an expensive, sophisticated and difficult to set up proportional typewriter COULD be used by a National Guard officer to type crude memos that no one would see for his personal files. Crafting that nonsense probably took hours as well.
CBS's analysts didn't authenticate the memos - they weren't asked to. My recollection is that teh analysts told Mapes thatthe memos were probably NOT authentic, but CBS ran with the story anyway.