Time the standard procedure but also record the time it takes to initiate action. Timing how long it takes to make the very first move may help understand how they are processing the information. I get a sense of the logic behind the arrangement. I am intrigued by students who misplace one of the diagonal blocks on Block Design. The next turn will do it, but instead the student flips the block over to the identical, opposite face and starts over.
Some kids rate several TTFs.
I then wonder about frustration tolerance, ability to stick with a strategy, etc. As with all such hypotheses, I then seek real-life evidence to confirm or refute my guess. Sometimes it is a unique response to the artificial demands of the test. Occasionally it helps me learn something about the student's operating style in other situations. Look to see if there were quantitative as well as qualitative differences as the task changes.