Timing was a joke teller's manipulation of the elements of a joke in relation to time. It had an effect on how funny an audience found a joke.
In 2365, Data told Guinan a joke and asked if it was funny, to which she replied that it was not, adding that it might have been his timing which spoiled the joke. When Data said that his timing was digital, Guinan found that humorous (i.e. that he, a Soong-type android, used a digital mechanism to regulate his own computer timing), but felt it would take too long to explain to him why. (TNG: "The Outrageous Okona")