The correct answer is A. 24.
Running staff should not normally be away from headquarters for more than 24 hours at a stretch. This is because they need to be available to respond to emergencies and to provide support to other staff. If they are away from headquarters for too long, they may not be able to do their jobs effectively.
Option B is incorrect because it is too long. Running staff need to be able to respond to emergencies and to provide support to other staff. If they are away from headquarters for 48 hours, they may not be able to do their jobs effectively.
Option C is incorrect because it is too long. Running staff need to be able to respond to emergencies and to provide support to other staff. If they are away from headquarters for 72 hours, they may not be able to do their jobs effectively.
Option D is incorrect because it is not a specific number of hours. Running staff should not normally be away from headquarters for more than 24 hours at a stretch.