There are benefits to writing each day. Not only will you get your book finished, but you will keep your unconscious mind thinking about your story.
Or are you waiting for that spark of inspiration? In my experience it only comes knocking when I’m writing. And that’s one of the reasons I write every day. The other reasons are many and varied from total absorption in my plot and characters, to being compulsive and determined to finish the book.
Of course, with everything else we have to fit into our days, writing, more often than not, will be the activity we can’t fit in. But even half an hour on a daily basis will be beneficial to your writing and your story. So if you can find a little window at some point during your day or evening, take it. Set a reasonable goal for the time you have and you will be surprised what you accomplish.
Earlier I mentioned your unconscious mind and I mentioned this because even with only a minimal amount of actual writing time each day, your unconscious mind will still be working away long after you have finished.