How early is too early when it comes to getting into a concert?

This is a little off topic but...

So I'm graduating with my associates degree in May, after 3 very long bumpy years. In the fall I'm going to get my bachelors. But to celebrate I bought myself tickets to the Lukas Graham concert. I am like completely obsessed lol. The place where the concert is being held said that it only seats 250, but can hold up to 500. All tickets were sold General admission and seating is a first come first serve kind of thing. My question is how early is too early to get to a concert? because I want to be like right in front of him.