How long to clear the 'suck zone' of a turbofan after start is initiated? I recently found this (IMO funny) picture. All funny and all. But let's make this a real situation.

Let's suppose I see my crush and his BF doing this, and I come with this 'genius' idea (alright, it's anything but a genius idea, but still) to start the engine they are sitting on. And no, I am not nice enough to turn the beacon lights on.

How likely is it that the engine gains enough suction to suck them in without they noticing it in time (considering the fact they need to standup and run for their lives)?

How long does it take for the engine to spool up enough suck a person in?
A start on a TF all the way to idle is about 20-40 seconds depending on the engine, and the fan itself won't do more than creep a bit until the core actually lights off which is 5-10 seconds, so they'll have lots of time to get down and get away as per @ymb1's diagram, once the wheeEEEEEEEEEEtickticktickticktickticktick starts.