The time to bailout depends on how badly the aircraft is/was hit
This is from Hap Hallorens account over Toyko: The Rover Boys Express was left alone over Tokyo in a cold and hostile sky. 5 crewmembers were in the aft section. Guy Knobel crawled back to the tail section to tell the five to bail out. The B-29 continued to be attacked by the fighters. Enemy cannon fire raked the fuselage from front to rear in efforts to bring the stricken aircraft down. Knobel found the tail section badly damaged with tail gunner Cecil Laird dead at his gun. The remaining three gunners and radar operator in back came forward. The ten Rover Boys that remained alive hurriedly prepared to bail out. The escape hatch was through a door in the deck of the front section. The door was opened with great difficulty and as they proceeded to the final step for bailout the nose wheel would not drop from the space as required to escape. The escape route was blocked. The forward bomb bay doors were open so the crew decided to open the entry door to the bomb bay. The crew could see Tokyo below the bombs that could not be dropped or jettisoned. The bay doors were not fully open but there was room to pass between the bombs and the doors. Bombardier Bobby Grace, his flight suit covered with blood was first to bail out. Flight Engineer, Willie Franz, was next to parachute out the bomb bay. Jimmy Edwards, pilot, was next to make his way through the bombs and into the thin atmosphere. Radio Operator Guy Knobel was next to parachute through the bombs. Hap Halloran tried to talk Aircraft Commander Snuffy Smith into jumping next but the bloodied pilot ordered Hap to jump.
The fuselage gunner's left and right bubbles say "Cut glass for emergency rescue"