Excel - Calculate Hours Worked - more detailed

I am developing an excel timesheet for my organization. I have two units A and B

Unit A :
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Work Start Time : 9:30 AM
Work End Time   : 7:00 PM

Tea Break Time 1   : 11:45 AM
Tea Break Time 1   : 12:00 PM

Lunch Start Time : 1:30 PM
Lunch End Time   : 2:30 PM


Tea Break Time 2   : 5:00 PM
Tea Break Time 2   : 5:15 PM

Paid Overtime Start : 8:30 PM

Sundays : Holiday
Alternate Saturday (1,3,5 - working): 9:30 AM - 1:30 PM, 1 Tea Break 11:45 AM - 12:00 PM


Unit B (Night Shift):
---------------------

Work Start Time : 9:30 PM
Work End Time   : 7:00 AM

Tea Break Time 1   : 11:45 PM
Tea Break Time 1   : 12:00 AM

Lunch Start Time : 1:30 AM
Lunch End Time   : 2:30 AM


Tea Break Time 2   : 5:00 AM
Tea Break Time 2   : 5:15 AM

Paid Overtime Start : 8:30 AM

Sundays : Holiday
Alternate Saturday (1,3,5 - working): 9:30 PM - 1:30 AM, 1 Tea Break 11:45 PM - 12:00 AM

This Units has a Holiday List defined by a Range specified in another sheet. There are different holiday ranges for different units

I want to compute the Hrs Worked between 2 dates by each employee excluding Holidays, non-working days (Sundays and alternate saturdays and half of working saturdays), and hours for lunch and tea breaks. For Unit B, the nigh shift complicates matters as it spans across 2 days (say if 1-Jan is a holiday, night shift folks do work till 1 st morning 7:00 AM and report only on 2nd night). The result excluding the Saturday complication is something should be something like :
Employee    Unit      Start-Date    End-Date   Hours Worked
------------------------------------------------------------
Employee 1| Unit A | 31-Dec-2008 | 2-Jan-2008| 16 hours (8 hours on 31 st and 2nd)
Employee 2| Unit B | 31-Dec-2008 | 2-Jan-2008| 16 hours (although the time extends to 3rd morning)

Pls help as this looks overwelhming. I do not know how to start