Calculating time using excel formulas

I have a question about calculating time to determine is a person is late in excel.

I am at a business where we process specialty eggs and have weekly shipments to different parts of the county. I am in charge of scheduling the the dock times for the trucks. We have an excel sheet where I put in the scheduled time (as AM/PM), their actual arrival time (as AM/PM) and the time they leave (as AM/PM).

What calculation do I use to show that if someone was late.

Example
Dock appointment: 8am
Acutal arrival time: 8:30am
Departure time: 9:30am

This exmpale shows that the driver was late by 30 minutes. How do I get the calculation to show that he was late (I want the cell to say the word late)?

Example:
Dock appointment 10am
Actual arrival time: 9am
Departure time: 10:30am

This example show that the driver was early by 60 minutes. How do I get the caluculation to show that he was early (I want the cell to show in minutes how much he was early)?