Of course, there are times when details can be a pest.
Luckily, I was able to fix the problem fairly soon. I found a calendar converter online. Put in, say, December 5th and it gives you the equivalent in a variety of time systems. And because I keep a list of the pages the different characters appear in, I was able to find those portions of the draft that needed alteration in short order.
Small details often get overlooked, but they are important for being another way of convincing the reader to be in the moment of the story. It's not only how certain characters tell time. The United States is the only country to officially use the U.S. dollar (actually, that's not true; Panama, Ecuador and El Salvador use it as well). You're not going to pay for movie tickets in Russia or Italy or Brazil with a handful of Lincoln slips. Distance is another thing. Americans are so accustomed to using the standard system of measurement (feet, yards and miles), but reading about a character in Britain loses it's believability if he doesn't use the metric system.
The solution requires no genius-level of intellect, folks. This is just a friendly reminder: get your little facts down right at the start of your writing so you don't waste time later as a fact-checker when you can be using it to refine characters, dialogue and plot; all those annoyingly important matters.
There's a flip side to this. Sometimes you can start a project with certain details appearing important, and then finding out that they are actually quite trivial.
Switch over to my outer space survival story. When you write a man-versus-nature story, it's necessary to know that environment and, in a sense, make a character out of it. This story set on a distant planet, I sketched out the climate, the terrain and even created a rough food web for different areas. Then, quite stupidly, I started writing more detailed notes on the plants and animals that the characters would encounter. This is a waste of time. Rather than do the Avatar thing and try fleshing out a planet in hyper-detail, I should have concentrated on the characters' spaceship and equipment.
Why? Why neglect the nature and focus on the technology? The best way I can explain it is this: take that same man-versus-nature idea and put it in a forest on Earth. A character doesn't need to know how the wolves around him socialize with each other. All he needs to know is that they are a threat to him. They can kill him and eat him. On the other hand, detailed information on the stuff in his backpack is more crucial because that's the stuff he depends on to survive.
When I was in grad school, we had a visiting professor from USC, a writer named Percival Everett. I asked him how he knew when he had done enough research and gathered enough information before starting a project. He said to me, "You just know." When you approach your work, plan ahead and figure out what material is most relevant to your needs.