I haven't been able to find a really date-specific start point, just "on a long train ride". But an estimate based on quick scanning thru some bio stuff would be around '97-'98. Here's some Bio -----
"The idea that we could have a child who escapes from the confines of the adult world and goes somewhere where he has power, both literally and metaphorically, really appealed to me."
Like that of her own character, Harry Potter, J.K. Rowling's life has the luster of a fairy tale. Divorced, living on public assistance in a tiny Edinburgh flat with her infant daughter, Rowling wrote Harry Potter and the Sorcerer's Stone at a table in a café during her daughter's naps — and it was Harry Potter that rescued her. First, the Scottish Arts Council gave her a grant to finish the book. After its sale to Bloomsbury (UK) and Scholastic Books, the accolades began to pile up. Harry Potter won The British Book Awards Children's Book of the Year, and the Smarties Prize, and rave reviews on both sides of the Atlantic. Book rights have been sold to England, France, Germany, Italy, Holland, Greece, Finland, Denmark, Spain and Sweden.
A graduate of Exeter University, a teacher, and then an unemployed single parent, Rowling wrote Harry Potter when "I was very low, and I had to achieve something. Without the challenge, I would have gone stark raving mad." But Rowling has always written; her first book was called "Rabbit." "I was about six, and I haven't stopped scribbling since."
For Rowling, the change in her fortunes has been slightly bewildering. But her daughter has no doubt about her mother's new career: when asked what mommies do, she replies without hesitation, "Mommies write!"