I found this in Starlog #2, November 1976:
"Bowie's "The Man Who Fell to Earth" is in current release—and garnering controversial reactions and reviews. Not one to wait for final results to come in, the natural-born alien is hard at work on his second sci-fi entry: Zero Hour, which will be made by British Lion Films.”
I haven’t been able to find any information on this film. Bowie worked on a few more movies in the 70’s but none of them were sci-fi. Based on the title it’s possible that this movie was going to be related to his song Space Oddity. It is interesting to note that British Lion Films was taken over by EMI in 1976 which might have lead to the demise of this project.