The longer a story becomes, the more crucial it may be to keep track of your timing. That’s not about the few seconds left before a bomb goes up, nor am I talking about mid-fight timing, but about the overall progress of time.
On the lowest level, you can only squeeze so much action into one day or one night – unless you choose an arctic winter setting or such – so, after a few chapters, you should know whether it’s time for sunset or sunrise. Still, that’s the easy part.
On the next level, you may have to ask yourself whether it’s Sunday or not. Again, that depends on the setting, but for a detective story, closed and deserted offices may offer special investigation opportunities.
I’m working my way up the timescale.
You can’t have full moon for three weeks in a row, nor can it return after six weeks. If you need the moon phases, you must keep track of your story calendar. If the tides are important to your story, you face a similar problem – high tide doesn’t take place on the same hour every day.
I’ve already mentioned arctic winter. In the northern hemisphere, you run into trouble if you need the long arctic night between June and August, just as you’ve thoroughly messed it all up if you need snow in Rome on a hot summer night. If your story runs several months, you better know WHEN you are.
I’m writing stories with sequels that span several decades. There’s no way to keep that all in my mind. I need to keep a calendar with the exact date per chapter. Only this way I can tell that my heroine has missed her birthday again.