Crystal Reports time calcualtion

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   hi everyone, 
I'm new to crystal report 2008, wish that you all can help.
I'm trying to create a graph chart using crystal report that using ms Access database. Below was the some example of database.
ID    Condition           Time              Floor
1          1              10:54:48 AM         1
2          1              10:54:48 AM         2
3          0              10:55:02 AM         2
4          0              10:55:16 AM         1

With these database, i'm going to calculate the time for each floor using the condition "1" and "0"( "1" for start time and "0" for end time). 
below was the basic theory for the calculation

(Floor 1 with time (10:54:48) and condition="0" ) - ( Floor 1 with time (10:55:16) and condition="1" )

and the result should be 18 second. the same goes floor no 2

(Floor 2 with time (10:54:48) and condition="0" ) - ( Floor 2 with time (10:55:02) and condition="1" )

and the result should be 14 second.

I'm sorry guy, it looked simple but i need to know how the formula is created for the calculation.