Computing Attendance Percentage

I have a class that will run from 6:30 - 9:30 p.m. and attendance is part of the final grade for the course. Is there a way to calculate the percent of time a student was present for class on a given day? For example, if a student shows up at 8:00 p.m. they were present for 50% of the class and will receive 50% attendance credit for that day.

Ideally I would like to input the arrival time of the student into one column then have the percentage calculated into a different column.

I'm afraid you won't be able to do that automatically.

If you are only worried about 100%,50%,0% you could use the late icon to mark 50% and maybe an additional icon for a different percentage.

If that would work for you let me know and I'll explain how to calculate the percentage.

I am familiar with how to use the icons just wanted to see if there was a datediff / timediff capability in the application.