1. Look for something else to bump first.
Especially if you are at the start of your project and haven't invested the time in that you have in other day to day items of your life, it may be an easy decision to skip writing. Once you start investing in your writing in terms of time and effort, it shows up higher on your mental to do list. It requires a re-think. Just because you've always checked your email three (or more) times a day, does that have to happen today? Perhaps you can take one of those times out, make something easier for dinner, short shrift a chore or put an errand off until tommorow.
2. Make sure you're being realistic about your scheduling.
If emergencies often come up, you may benefit from building some more margin in your schedule. Margin is the space in which you plan realistically (so you don't have to speed to get to your appointments on time) and leave a bit of extra wiggle room for the unexpected (a train, a long line, your child forgetting their lunch). Virtual coach and author Michael Hyatt has a free ebook on creating margin that is well worth the read.
3. Do whatever you can on your project no matter how small.
When you come up to a day that's especially off the wall or a schedule you are struggling to reduce, don't lose hope. Remember that small incremental change can still completely change your life, begin daily writing practice, and produce a book. Be as kind to yourself as you would a friend and use that saved emotional energy for the writing.
Your writing deserves to have top billing in your daily schedule. You have a message, a story, or insights to share. You don't have to be leading the ideal time abundant life to make that happen. These few tweaks to your day and tommorow will be another story. And with practice and progess, next year even more so. Remember your top priorities. Don't let what's happening today determine if you will get to them. Make your top priorities your top priorities.