How long before you leap an AFK'd camper?

[HawkMasterson1999]

Lets say you roll up on Hadden spawn or some other static spawn with a long repop and there is a guy standing close by as if he's camping it but he's not moving or casting or taking any action. How long should you wait before you take his spawn? What do the rules say and what do people think is a polite reasonable amount of time? Obviously you can't expect to keep your mob if you're AFK. Am I wrong?