Summing time is possible in Tableau, there are a few approaches. This link will show you one of them: Re: Using Time (Hours, Minutes, Seconds) as a Measure
There isn't a clean way to do this but converting all of your time periods into seconds, then summing, then allows you to mathematically convert the summed seconds back to hours, mins and seconds.
Andrew Watson thanks for the reply Andrew, but I want to calculate the difference of hours, mins and secs between two fields and then up the hours & mins & secs.. that was were i was running into problems. The two fields were ( [Evnt End Time] - [Evnt Start Time] ) if you can please assist me how to calculate the difference and how to add up the hours, mins and secs would be appreciated .
Can you Datediff to find out the number of seconds difference, then do a calculation to convert the seconds back to hours, mins and seconds?
DATEDIFF('second',[Evnt Start Time], [Evnt End Time]) to get the difference in seconds.
This link shows how to convert the seconds to hours, mins and seconds: Converting Seconds to HH:MM:SS or DD:HH:MM:SS | Tableau Software