Success as a lawyer often requires the ability to handle a certain amount of pressure. Timed exams are one way of screening for that ability. But it's by no means a sure-fire predictor of success: Legendary trial lawyer Joe Jamail [0] flunked his first-year Torts class at UT Austin [1], yet went on to become a billionnaire.
[0] https://en.wikipedia.org/wiki/Joe_Jamail
[1] https://abovethelaw.com/2015/12/r-i-p-to-a-billionaire-lawye...
¯\_(ツ)_/¯
(I never met Joe Jamail, but by reputation there was a lot about him that I didn't especially admire.)
But it's beyond rational dispute that Joe Jamail was one of the most successful trial lawyers of our era.