I know the driver's edge here in tx require novice drivers to use street tires. Street tires are good for about 15 min for the most part. Which explains why they limit the sessions to 20 min.
Anyone can drive for 30 min. Again, the concern with the groups I drive with is safety. I know I would not be doing very well past the 20 min mark when I was a beginner. You're in sensory overload the entire time.