TimeSimplicity & Other Product Ideas

We have a client that pays a shift Differential if the employee works at least 3 hours after 4PM.
We use this code to change the punch category right now:
if(istimes and outispresent and Hours >= 3 and intime >=4:00pm and (employee.home2 = "SHDIFF15" or employee.home2 = "SHDIF15"))
   {
   category = "SHDIF15";
   }

The problem is that sometimes we have an employee punched into 1 department (location) from 4PM to 5PM - then another dept from 5PM to 7PM. Since the total hours after 4PM is 3, they should get the SHDIF15 category. Can a function be added to the scripting language that could calculate the total hours worked between 2 times for the current day? example   HrsAfter4 = HrsBetween(4PM,11:30PM)