Although this is a common expression, it is technically wrong. The accurate statement would be:
"Its predictions were correct 88% of the times." (note: plural "times")
One of the meanings of "time" is "an occasion". That is the meaning used here. It has nothing to do with the kind of "time" that a clock measures. Here are some examples of "time" used with this meaning:
"Last time I saw you, you looked sad"
"Every time you sing, you put a smile on my face"
"Half of the times I have seen Mary, she looked sad"
"88% of the times he made a prediction, he was correct"