Time Clock Question

[savagenoob]

I have some code that clocks people in and out, then a report that calculates thes time between clocks in and out and outputs the result. How I currently do this is everyone that every clock out I calculate the minutes since last clock in and input to database. Then when the report is pulled I just do a SUM() of that row and voila, I get total minutes clocked in... BUT, I need to add a function that allows the admin to add a clock in/out just in case an employee messes up and doesnt clock in/out. The problem I am having is how to calculate the minutes without automatically calculating the minutes when they clock out, since I will be inputing user generated timestamps this no longer will work... any PHP genius know of a way to effectively do this?