When does Geronimo (1939) happen?

Never in real life, of course. The events are fictional.

The fictional date of Geronimo (1939) may be from about August 1876 to about February 1877. Watching it, I noted the newspaper articles about Geronimo's rampages at the beginning were dated to 1875 and 1876. An article dated August __ 1876 said President Grant was sending General Steele to Arizona. After the main characters come to Arizona there sems to be a time skip of six months which should go to about February 1877. Then the main action happens. So if I noted the newspaper dates and the internal passing of time correctly, Geronimo (1939) should happen from about August 1876 to about February 1877.

Since President Grant awards a medal of honor at the end, and since his administration ended on March 4, 1877, Geronimo (1939) must end before March 4 1877.

And of course the movie's events never happened in real history!