I have a slightly different way of doing it. I ask people what time they are arriving. Why should I be home at 4pm, if their flight does not arrive til 8? I can go on about my day and look forward to meeting them at 8pm. If someone calls in a reservation I explain that I need their check in time as I plan my day around them and I want to make sure I am here when they arrive. I still get some people who show up really late, but they have been warned that I may not be available if they miss the time they gave me.