If you don't have time to write, that doesn't mean you have to ignore your book or screenplay. Here are a few things you can do to keep the project alive in your mind (this is for works of fiction, but I bet you can think of similar things you can do if you write non-fiction):
* Imagine one of your characters is with you as you go through your day. How would he or she react to all the things that happen? You'll get to know the characters better and when you do sit down to write again you'll find it much easier to know what they'll do and say.
* At the start of your day, decide on one scene or part of the story to think about, and then just get on with your day. You will find that your subconscious mind keeps working on it anyway and new ideas will pop out at unexpected times.
* Take five minutes a day to think about the project and jot down any new ideas. Don't try to force it, some days you'll have lots of ideas, other days you may not have any. That's fine, just make it a habit and I think you'll find it useful.
As well as producing ideas you can use when you have time to get back to writing, these will banish guilt about not writing every day.
HOW TO FIND MORE TIME TO WRITE
Along with using these methods, you may want to try to find some more time to write. A few ideas:
* If you normally eat lunch at your desk, once or more a week go to nearby coffee shop where you won't be disturbed.
* If you regularly watch some TV series, give up one of them.
* One or two days a week get up an hour early (or stay up an hour late).
* If you have kids, swap babysitting times with a friend or neighbor so each of you gets a couple of hours at a time undisturbed.
(Do you think you might profit from having Mark Twain, Jane Austen, F. Scott Fitzgerald and a hundred other classic and modern masters of writing giving you their advice about writing? You can find it in my book, Your Creative Writing Masterclass, published by Nicholas Brealey and available from Amazon or your other favorite book seller.)