Of course it's great to have a period of two or three or four hours of uninterrupted writing time, but here are ten things you can write when you have only ten minutes or even less:
1: A haiku. In case you've forgotten the details about this Japanese form of poetry, the pattern of haikus in English is three lines, the first with five syllables, the second with seven, the third with five.
Traditionally they are about images or feelings relating to nature, beauty or an important moment but feel free to add your own variations. For instance, if you were to write a haiku about your project, what would it be?
2: A description of a character in a book, script, or story you want to write. You can focus on the physical for one session, the emotional for another, the childhood and family for another, and so on.
3: The kind of glowing review of the project you're working on that you hope to see when it goes out into the world. Be specific--what makes it so wonderful? This can serve as a guideline for you when you create and refine it.
4: A thank you note or email (a note is better) to someone who has inspired you or who gives you moral support for your creative activities. Is it your spouse or partner, or a parent, a sibling, a friend? Do you think 'oh, they know already that I apprecate them.' Are you sure?
5: A note to yourself about what you need to do next to help bring your creative idea or project to fruition. If it's a big task, break it down into a list of smaller steps and the order in which it makes most sense to do them.
6: A list of at least ten things you've achieved in the past despite initial doubts. Keep it handy for days when you doubt yourself.
7: A description of one place you were in the past 24 hours that might be a good setting.
8: One memory that makes you smile.
9: One memory that doesn't.
10: One thought about a story you might want to write in the future. If you do this in a notebook you carry or a notes app on your phone, over time you can accumulate lots of ideas.
Some of these might fit into a particular projects, some won't, but all of them can keep you exercising your creativity and developing your writing skills.