Or so a patent lawyer told me, anyway. It's possible I misunderstood something.
A much better way to establish priority is to file a provisional patent, good for a year.
The book "Patent it yourself" makes good reading - not as good as working with a patent attorney, but a lot cheaper.
Sans getting it notarized, of course. But that costs time and money too.
Or can you fake the date with Gmail? If so, know of a possible alternative? I'll probably end up using it.