Date and Time difference between date range

Greetings All,

I am required to calculate the difference between two dates and two times in HH:MM:SS format.

a.In my infoprovider I have only Date and Time as keyfigures.

b.An indicator I and D differentiates as Start Date (indicator = I) and End Date (indicator =D), similarly start time and end time. This was done in BEx.

Now, I need to calculate the difference between two dates and times in HH:MM:SS format.

I have tried the TIME() function as below and it is giving me wrong results.

=TIME((End date - Start Date)*86400)) + TIME(( End Time - Start time))

Kindly share your inputs. Thanks in advance.