Requesting a diagram of the apartment, what does Juror #8 go on to prove about the 15 seconds the old man says passed until he saw the boy run out?

After a brief argument, 8th Juror brings into question whether or not the downstairs neighbor, an old man who had suffered a stroke and could only walk slowly, could have gotten to the door to see the boy run down the stairs in fifteen seconds, as he had testified. 8th Juror recreates the floor plan of the apartment, while 2nd Juror times him, and they conclude that he would not have been able to reach his door in fifteen seconds.