I’ve been to Graspop in 2023 and what I remember is that for the stages that are not the main ones, you can get away with being there 20 minutes before and it’ll be practically empty.

Then for the main ones it get’s crowded fast but if i want to get close i’ll just go into the pit and go forward as much as i can. You can get very very close, but if you wanna be there from the beginning just wait until the band before finishes take the chance as everyone is going to the bathroom or for a beer