How early should I go to a concert with general admission tickets?

I have general admission floor tickets to see a concert at a venue with a capacity of 5000, and I believe the show is near sold out. We were originally going to leave at around 1pm to get there at 1:30-2:00. The doors open at 7 and the show starts at 8, we want to make sure we get a good spot and we also don't want to wait in line to buy merch for too long. Are we leaving too early? What time would you recommend going at?