I often leave notes while I'm writing. Sometimes it's notes that I don't like the words, sentence, or even the scene, other notes could be about a character's motives, or things I want to elaborate on later. The most common note I see in my work in progress (WIP) is 'What time is it?'
It might not be a question your reader needs the answer too, but as a writer, you need to know. If something is off about your timing, the reading will pick it up. Only so many events can happen in a day.
When I start my first draft, I decide what day it will be in the story and use the Microsoft Word comment feature to note it. Every time the day changes, I note it in the manuscript so I at least know what day I'm working on. This is important because weekends can throw a wrench in your plans. Not everyone works on weekends and many offices are not open on weekends. If your character is working seven days straight for no reason other than you forgot to give them a weekend or a day or two off, your reader will notice.
After I finish my first draft and reorder my scenes/sequence of events, I put the events into a calendar to give me a visual of when things happen. I find it useful to keep track of everything.
Once I start my revisions, then I worry about the time of day. I'm usually pretty good about keeping track while I'm writing, but once I shift things around, I need to make sure everything works. In my current WIP, they are searching for something that only comes out at night so it would make no sense if they encountered it during the day.
Keeping track of the time of day helps you move your story along and by generally knowing if it's morning, late morning, early afternoon, mid-afternoon, evening, etc., you can add flavour to your story and settings. Maybe it's late afternoon and your character is starving because she missed lunch or is fighting rush hour traffic. Maybe your character can enjoy the peacefulness of an early morning. Use the time of day to build your story and setting.