When I used to fly UA, I'd get emails about schedule changes months in advance. This was as far back as 2004, BTW.

AS should send email notification every time there is a schedule change of more than 30 minutes. This would include a smaller schedule change that results in a misconnect, thus requiring re-booking on another flight.

That way, you don't get emails saying your schedule has adjusted by one minute, but it would keep people abreast of more significant schedule alterations.