Advice required. Just tried to check into my BA flight from Miami to LHR and they are saying an 18 hour delay. So do I still need to be at the airport in time for the original departure time or will I have classed as a 'no show'
Unfortunately, the offical requirement is to be on time for the original scheduled time, as annoying as this may be.
The reason is that the delay might disappear partly or completely (the spare part came earlier than expected; another pilot volunteered; repairs went faster than estimated; whatever), and then they will fly without you, and you missed the flight and have to bear the consequences.
If you can get in contact with them, they may confirm that you can come later (and I recommend to ask them to email you this for reference). Otherwise, you play at your own risk.
This happened to me before, and the rule is you have to be at the airport at the original check in time, irrespective of the actual flight departure time.
There are many reasons for this, but the primary one is that the check in desks are not manned permanently. Staff from BA (or its agent in Miami) are only allowed to operate the check-in desks for a specific period of time - usually from 3 hours before scheduled boarding till about an hour from boarding.
Once this window passes, the counters are emptied and another airline is takes over. The only exception to this rule is if you are flying from the home base of the airline (so if you were flying from London to Miami, it is possible for you to check-in earlier at London since there are dedicated, permanent BA check-in desks).
At some airports (this doesn't apply to the US or Europe but adding for completeness) the immigration counters also have a set time during which a flight is "open" for processing, due to security concerns.
So given all of the above, the you should not gamble with the timings. Arrive on time for your original flight, check in and drop off any luggage. You can then choose not to go through security until nearer to the time of your flight.
As you are already checked-in and have surrendered your luggage, you can leave the airport and come back and go directly to the security queue.