Re: JK Rowling to revisit Harry Potter-verse for new movie series
Rowling said '70 years before the events of the HP novels', which means the 1920s.
Regarding the content of this series, all indicators are that it's going to be an entirely original work that just happens to share the title of the in-universe textbook/for-charity sourcebook. It's essentially and effectively a brand-new HP-related novel series, but in the filmic medium as opposed to the literary one.
Assuming the films are meant to be 1991-1998 as well, and that it's fully 70 or more years before them.
"But there's no sense crying over every mistake. You just keep on trying till you run out of cake."