Nobody thought it was possible...

Yesterday, Guns N' Roses started their show at Graspop 20 minutes early. I even missed the first song because I was still in the marquee for Children Of Bodom.

Did they tell Axl their start time was two hours earlier than the actual start time? Did they finish their set?

That was the first thing that came to mind, yeah :)
They were scheduled to play from 22:50 until 01:30 and they played from 22:30 until 01:30. 3 hours, yes.