The best time to start writing is when you have enough time.
The best time to start writing your book is when you have enough money to afford free time.
The best time to start writing your book is when you have the support of your family so you can allocate a part of your free time for writing.
The best time to start writing is 5 am when everybody in the house is still sleeping.
The best time to start writing is 10 pm after everybody in the house is sleeping.
The best time to write was before you opened your browser, visited this website, and read this article.