It is not an AD issued by Boeing. It is a Safety Directive. And it has to be implemented within one week. Until then the airplanes that do not comply stay on the ground pending repairs.
Needless to say it is a 24 hour job. But the plane WILL BE GROUNDED until it is implemented!
That's nonsense.
Either the aircraft is grounded [it isn't] or there is a deadline on compliance with the AD, there wouldn't be any point in doing both.
US-registered 787s subject to the AD can legally fly for 7 days (from the AD effective date of 5th December) before action to ensure that the lockwire installation is correct, and for 21 days before ensuring correct assembly of the engine fuel feed manifold rigid and full flexible couplings.
If operators elect to action the AD before the deadline then that is up to them, but until then they can continue to fly the aircraft if they wish.