It just means that 88 out of every 100 predictions were correct. During the entire time it was asked to make predictions, it was accurate 88% of that time. Simply emoving the phrase. (The predictions were correct 88%) makes no sense.

I may not seem to make sense, but the sentence doesn't work without 'of the time'. Without that, we don't know exactly what the 88% refers to. Maybe it means the predictions are correct within a 12% margin of error. Another way to think of it - - - what question is being answered here? How often were its predictions correct? So we need 'of the time' to answer that.

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"

The English word of has meaning meanings and ways of being used. https://www.merriam-webster.com/dictionary/of Definition 2 E 2 e : occurring in a fish of the western Atlantic Can be translated in your scenario to 88% OF the time. = how often how many times to what degree of accuracy. = in 88 out of 100 times the results were correct. If you change the sentence to say "it's predictions were correct 88%" It makes no sense, you would still have to include the word 'OF' either at the beginning or end of the sentence. "In 88 out OF 100 runs/results/attempts/trials/ etc its predictions were correct".