Qualifying Procedure
On a given day of qualifying, the track is open for qualifications from 11 a.m. (or 12 noon) to 6 p.m. local time. If there are no cars in line to make an attempt, the track is opened for general practice. The busiest periods of qualifying, due to ambient and track temperatures, are the first hour and the final hour. Due to the lower temperatures and shadows along the track it is common for drivers to wait until late in the day to make their attempts. The car must be moving out of the pits before the 6 o'clock gun for the attempt to count.
Read more about this topic: List Of Indianapolis 500 Pole-sitters