You can pre buy your tickets for Fork & Dine a few days prior to when you want go see the show - typically whenever the last big release day is they'll set the schedule until the next movie release day.
I did that when we went on a Wednesday during our last trip - I purchased them on that Sunday. You should be able to go through the AMC site & it will take you to where you can purchase tickets.
Splitsville has a way online where you reserve lanes as well through their party request form.
Both are super fun. We did Splitsville in July & October. I've done Fork & Dine twice - once in March 2012 and this last trip.
