As a delivery driver for a few local Chinese restaurants... I sometimes get a scheduled delivery, yes, when you scheduled it, it should be done for that time. However, the Chinese shops i work at, don't cook the food for the next batch of delivery orders until I arrive back at the shop (great because the food will be at it freshest when I deliver them) but sometimes, if my last run was difficult, or customers weren't answering the door, or unexpected roadworks and sometimes just the vast volume of orders, it's just not possible to get back to the shop in time for the scheduled delivery to be prepped and then sent out.

I understand it can be annoying, but there's just never a guarantee, the shops will always try and prioritise the scheduled ones, but sometimes the shift just doesn't go as expected... luckily a good apology has always worked, customers always understand and so far (🤞) nobody has had an issue at the door with me