I wrote a book and had it published in another state in 2017. It will be distributed worldwide and may make money in the future. At what point in time do I enter it?

Once it generates reportable income.  When that happens, you will have what is known as royalty income, which for you is reported on Schedule C.  You will not have this item on your 2017 return (this year).  However, for more information on this subject, please see this FAQ to prepare for the future:  https://ttlc.intuit.com/replies/4792182