When Does the Mixed Live-Action/Animated Film "The Incredible Mr. Limpet" (1964) Take Place?

"The Incredible Mr. Limpet" is a comedy fantasy historical fiction mixed live-action/animated film written by Joe DiMona with Jameson Brewer and John C. Rose [adapting "Mr. Limpet" (1942) by Theodore Pratt] and released March 28th, 1964. 

It takes place in the years: 

1941 AD - 1945 AD 

We know this because, in the frame story, United States Navy men George Stickle and Admiral Harlock reopen a file labeled "SEPTEMBER 1941" in a room labeled "TOP SECRET. Both characters refer to "September, 1941" as "when it started" or "that's when it first started". Harlock also says, "we locked this file back in 1945", implying the point the file's contents were last updated. 

Furthermore, a "1941" calendar open to the July/August/September page is visible behind the water cooler in the Brooklyn naval shipping office where bookkeeper Harry Limpet works. 

At almost halfway through the movie, the famous and tragic attack by Japan on the U.S. Pearl Harbor naval base in Hawaii is mentioned in a radio news broadcast stating, "the incredible news this morning of the unprovoked and dastardly attack". The Pearl Harbor attack occurred on December 7th, 1941 AD in the real world. 

In the conclusion of the main action, the passage of time since the start is unclear HOWEVER the Navy locked the Limpet file in 1945 AD, as revealed in the frame story. Plus, a newspaper front page displayed on the screen boldly says "VICTORY". Presumably, this is announcing the real-world V-E Day, which was May 8th, 1945 AD. 

Additionally, there is a frame story complete with prologue and epilogue set in an unplaceable 'present'.