Since the time travelers saw everything relative to the geographical position of the Planet Express office, there's no way the Professor could have shot Hitler.
It was implied the professor got out of the ship the first time and travelled to Hitler.
The second time around he fired from the ship which is why he missed.
It was implied the professor got out of the ship the first time and travelled to Hitler.
The second time around he fired from the ship which is why he missed.
All life on Earth, including plants and phytoplankton, went extinct in the year 1,000,000,000, making it impossible for Fry and Professor to breathe.