You are space available to the interview which means exactly that. If there is space available, you can have a seat. You also go behind pretty much everyone else except on RAH aircraft, then you just go behind us IIRC. Getting to IND is a notorious PITA for interviews. I understand that the company is pretty good at getting you rescheduled if you don't make it. If you are withing 3-4 hours of IND, I'd highly recommend you just drive.