Experience makes me skeptical of taking these delay notifications at face value, though my formative experiences in this context were non-BA. Not once, but twice, on United I received delay notifications via text or email, showed up at the airport commensurately late, and found the problem had been quietly fixed, they had boarded whomever was around, and just left. I never had a message to report status change. Since then I turn up when I was planning to, whatever the carrier, delay notice or none.