Theoretically, if an average English speaker had the name of each U.S. President perfectly memorized, he could recite the list in somewhat under a minute. This figure is based on the overall number of presidents and National Center for Voice and Speech average speech rate estimates.
There have been 44 different presidencies, but only 43 different presidents have served because Grover Cleveland was elected to two non-consecutive terms. The National Center for Voice and Speech estimates that an average English speaker is capable of speaking 150 words in a minute. If half of the presidents have two names and half of them have three, someone naming the presidents would have to say around 110 words.