Time evaluation Standby OT rules

I have problem regarding the Overtime calculation rules in Time Evaluation. Right now in Schema, Overtime rules are setup based on Availabilty of an employee on a particular.

If employee is available (In infotype 2004), then all Overtime calulations are applies different calcuation rules, If employee is not on standby then different rules applies.

At the moment i setup IF Function check VASTP2004 for Availabilty

IF

VARSTP2004

N (No) then SCOND=F IF

Y (yes) then Scond=T If

But requirements has been changed and user wants the overtime calulation based on exact number of hours in infotype 2004.

Ex: If employee is Avialbe in infotype 2004 for 30/03/2010 from 10:00 to 22:00, and did overtime from 06:00 to 09:00 and 20:00 to 22:00, then morning OT 06:00 to 09:00 should apply to non availabilty rules and 20:00 to 22:00 should apply to Availabilty rules. This is simple example i am giving to understand but there are some rules are there.

In this case how can i use the IF function to read the current TIP entry table to check the condition of availabilty times . If the time pair falls in availabilty hours it should process some set of PCR else should process different rules.

Any idea how to read TIP (time pairs) using IF function along with Operation SCOND.