Calculating Business Hours

[legendary_popsicle]

Hello again! Another (probably) difficult problem that I need a solution to. I am developing a spreadsheet which calculates when a certain task should be completed in terms of business days. For example, the task below needs to be completed within one business day:

M1: Start Date
M2: 7/27/2011 5:54:05 AM

N1: End Date
N2: 7/27/2011 12:35:18 PM

O1: Projected End Date
O2: =WORKDAY(M2,1,Holiday)+MOD(M2,1) (which would be 7/28/2011 5:54:05 AM in this case)


So the formula above works perfectly for tasks that need to be completed in terms of days, or full 24-hour increments. However, what if a task needs to be completed in 3 hours?

I need a formula that can calculate a projected end date in business hours -- so that it would exclude hours between 7pm and 7am, weekends, and holidays. Any way you guys can help would be amazing. Thanks in advance!

 

[legendary_popsicle]

I found a formula in another thread and modded it for my purposes. Is there anything I am missing? I'd like this to be tight as a drum.

=IF((MOD(A2,1)+0.125)>0.791666666666667,INT(A2)+IF(WEEKDAY(INT(A2))=6,3,1)+0.291666666666667+0.125-(0.791666666666667-MOD(A2,1)),INT(A2)+MOD(A2,1)+0.125)