It would need launch, rise up 3 feet, fly, out of 4 directions, one direction right toward him and then, if he'd not already moved, lower down 2 feet and then it would hit him. I'm getting about 4 seconds with some pretty crazy ninja moves.
Or, it could be one in a billion and DJI's programming could be completely ignored and instead of launching up 3 feet the Spark could, out of 4 directions, pick that one direction toward his face and fly, at full speed, right toward him at full speed. Perhaps 1.5 seconds. Here is a better question.... what are the odds of that happening? If you went out right now and launched your Mavic in the same conditions, let me know how many launches it takes before it auto launches one that one side without lifting off a foot from the ground. It's so risky I'm guessing it should not take you long to get it on video.
Or we could come back to reality and say it would be something like one in a billion. Of course we'd not be able to act like he about killed himself for being so reckless. No... we'd not be able to act so outraged on a public forum.
Edit:
From iJustine's video:
View attachment 13785
She's about to kill herself with the Spark! How terrible and irresponsible! Look how close it is to her head! It could leap to the side and smack right into her face. She's horrible. People like this should not be allowed to have YT channels! She should be nothing but perfect!