I have done this a few times and there is just no way of knowing how popular an act will be so I would suggest getting there right at opening so you can have your choice of times. If you look on the app or website, it should give you opening times for the day you want to go - I believe it's 11 am, but I would double check that. This most likely means lunch on the earlier side.
We have done this, as well, for more popular acts in lieu of Regal Eagle - we always choose Spice Road Table (least expensive of the reserved dining) - the food is great and the portions are quite large for "small plates".