In the unlikely event that your order contains different partner function, where does the system check the information to know if the customer accepts delivery on a certain day and time?

Delivery scheduling and goods issue date checks are performed at the Ship-to party level because that's where the delivery location and transportation calendar are maintained. The Ship-to party's master data contains the specific unloading point, transportation zone, and delivery calendar that determine whether delivery is accepted on a particular day and time. The Sold-to, Payer, and Bill-to partners don't control these logistics parameters.