I would trust that message, particularly if HBO and you can keep half an eye on status via the App (etc). Clearly if your marriage depended on being on that service then you would recalibrate the risk matrix accordingly. Otherwise it's great to be given this sort of useful information. There is a variation of this which does NOT change the check in time - particularly for out stations (more out of lack of knowledge of how the ground agents are going to handle matters), but you did not get this. So enjoy the sunshine!

(BA55 is LHR to JNB for those of us who haven't memorised the timetable).