You should tell people if you're going to be late.
Demi has dinner plans with her cousin, Karla, at 7pm tonight, but needs to go grocery shopping.
Demi wants to do her grocery shopping before dinner with Karla.
Demi tells Karla that she needs to get groceries and asks if they can push dinner back by an hour.
Demi is still shopping around when she sees that it is already 7:30, but figures Karla won't mind a bit of a wait.
Karla agrees, and she and Demi enjoy a nice dinner later on in the evening.
Karla didn't think Demi would show, so she left the restaurant.