It isn't perfect and does change quite frequently, but I've found FR24 tends to be accurate more often than not and gets the info out sooner. My flight from Porto last week was noted as delayed in FR24 long before BA had updated their app.

If you haven't got it, the CheckMyTrip app is good for that sort of thing as it sends you notifications with any updates, though that being said it can sometimes be a tad grating to see a notification of "departure changed from 21:20 to 21:27" or something like that.