Pickup Not Ready at Scheduled Time

I placed a pickup order for a Mac (not one of the new ones), and I scheduled the pickup for 6:15. It’s 6:22 and the staff won’t let me pick up my order because I didn’t receive a text message from Apple stating that the order is ready. Why is my order not ready if I specifically chose a time to pick it up? I have things to do outside of waiting at the Apple store, and I don’t think it’s fair.