"
> You have an outline
> and proposal for such a design, which is a big step
> forward, but the devil is in the little details.
I believe I've worked through all those little details over the
last year and a half while coding it, and there were a lot of them.
The functional details are not covered in the paper, but the
sourcecode is coming soon. I sent you the main files.
(available by request at the moment, full release soon)
"
- Satoshi
https://www.metzdowd.com/pipermail/cryptography/2008-November/014863.html
Date: Mon Nov 17 12:24:43 EST 2008
A year and half earlier would be:
May 17 2007
So he was inspired to begin working on Bitcoin on or before that date.
Often it's said that Satoshi was inspired by the 2008 financial crisis and the ensuing bailouts (which he cites in the genesis block), but this claimed start date is much earlier.
He was probably inspired by the initial subprime mortgage crisis, which began in February 2007. (The US housing bubble popped in mid-2006.)