Within the first hour of the doors opening. Usually stays pretty open until the main band plays.
For the show I went to, people started lining up the night before, though technically I believe they weren't allowed to until 8am, the day of the show. If you go an hour or two before it starts though, you should be able to get in the front.
I had a seat number and was required to sit there. I was in line for about an hour to go in the venue.
I got there an hour early for my 9 pm show and was in the front row.
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