When you purchase a Lightning Lane, do you get to pick a time slot? Or do you just get the next available time slot?

We’re landing at around 8:30 AM. I may want to drive to take my daughter to Cocoa Beach first to look at the cruise ships and grab a lunch at Rusty‘s. Then come back and go to Epcot. I’d like to time my Lightning Lane for later in the evening. Is that a possibility?