midnight
The groups of three might spend two hours , even three hours , he told them , so long as they performed their task without making a noise that would attract the attention of the sentries on either side . The darkness of the line , from the shadows of the trees and bushes and the deepness of the cutting itself , Max felt he could rely upon to prevent the other sentries from seeing if aught were amiss . The important thing , therefore , was that they should perform their task without noise . Promptly at midnight the sentries were changed . The momentary bustle was , as arranged carefully beforehand by Max , taken advantage of by the groups of three to creep close up to their objectives . Then things settled down again in quietude . All was peaceful and silent between the thunder of the trains , and time was allowed the sentries to grow accustomed to their surroundings and to develop any individual habits of carelessness that might be theirs .