I imagine there will be absolutely no bleeping about from the festival organisers if there is a whiff of Jack running late, I have been to a lot of festivals in my time and have seen stage managers hurry up late running acts people actually wanted to see, never mind a slop goblin piggy backing on someone else's slot. Different festivals but it's been done to Mystery Jets, Eagles of Death Metal, Lacuna Coil and I even saw the stage manager just cut the amps and mics of Airbourne for climbing the stage rigging in the rain, when they had plenty of time left in their set. Unless you're Axl Rose with an over running afternoon nap and you're headlining the day, there's no mercy.