Bocchi arrived two hours ago, as shown via the text message, but he somehow didn't notice the message. Then, being the timid character that she is, she was too intimidated to knock on the door or ring the bell, meaning she had to sit out on the front step for two hours, hoping he'd check his phone, as the pizza slowly grew cold.

Additional note to this: there's blood coming from the neighbor's door in the hallway, implying Bocchi was possibly forced to witness a violent crime during the time she was waiting for the customer to open the door.