What does the river give Montag time to do

The river gives Montag the chance to escape.

He tossed his own clothing into the river and watched it swept away. Then, holding the suitcase, he walked out in the river until there was no bottom and he was swept away in the dark. He was three hundred yards downstream when the Hound reached the river. Overhead the great racketing fans of the helicopters hovered. A storm of light fell upon the river and Montag dived under the great illumination as if the sun had broken the clouds. He felt the river pull him further on its way, into darkness. Then the lights switched back to the land, the helicopters swerved over the city again, as if they had picked up another trail. They were gone. The Hound was gone. Now there was only the cold river and Montag floating in a sudden peacefulness, away from the city and the lights and the chase, away from everything.