Crystal Reports Formula

Message

   hi guys,

i want to create a chart that based on "count of Time by Floor and Condition" using  the database below. However, i need to create a formula to calculate the "time field" before add it to the chart. 

(time in condition =0) - (time in condition =1)

0 refer to end_time.
1 refer to start time.

if you guys knows how to create a formula for the above "logic formula" please teach me how to create it.

ID---Condition -------Time---------------Date---------Floor

1 ------ 1 ------- 10:54:48 AM ------- 2/21/2008 ------ 1 
2 ------ 1 ------- 10:54:48 AM ------- 2/21/2008 ------ 2 
3 ------ 1 ------- 10:54:51 AM ------- 2/21/2008 ------ 4 
4 ------ 0 ------- 10:54:52 AM ------- 2/21/2008 ------ 2 
5 ------ 1 ------- 10:54:58 AM ------- 2/21/2008 ------ 3 
6 ------ 0 ------- 10:55:16 AM ------- 2/21/2008 ------ 1 
7 ------ 0 ------- 10:55:31 AM ------- 2?21/2008 ------ 3 
8 ------ 0 ------- 10:55:45 AM ------- 2/21/2008 ------ 4 