We did the dessert seating the week prior to your dates last year, on a Thursday night. The line started by the churro cart before the podium arrived at 5:50pm for a 8pm check in.
Be sure to have someone in your group arrive early for best seats; seats are assigned first come first served.
It was crazy busy, once you are in NOS area, don't leave.
It is too hard to navigate the crowds. Go ride HM or sit and people watch. CMs will be out doing crowd control and it can be hard to get to your assigned area.
If you have the early show you can get seated by 8:30 and start enjoying the seat, goody box and drinks.
You are also allowed to stay for the fireworks
IMO the first show is worth the $ because you get to stay seated for the fireworks and they will still serve you drinks

another option fo picking up your tickets is Guest Services located outside the park to the left of the entrance. Not much of a line there compared to city hall

and like everyone else said be sure to call at 30 days at 8 am sharp!