System = actual hours keyboarding and/or audio playing. It is NOT just having a report on your desktop.
If you take 2 15-minute breaks per 8-hour shift x 5 = 2.5 hours difference between webclock and system hours, permitted. Part time 20 hours weekly = one 15-minute break per 4 hours worked.
As long as there is no more than a 2-hour difference for a 40-hour work week, you should be okay.