I've been working on the same thing recently. Don't know if you are still interested in an answer from a question from TWO years ago (I guess the Tableau wonks aren't into running). Anyway, what I found out is you have to break the time data down back into it's lowest common denominator, in this case as you pointed, seconds. Since Excel (I'm assuming you're using an Excel file for your data source), stores all time from a baseline date, I had to use DATEDIFF to arrive at the right time. First, Tableau's baseline date is 12/30/1899 12:00:00AM. So I created a dimension called Start Time with one entry #12/30/1899 12:00:00 AM#. Then created a calculation using DATEDIFF('second', [Start Time], [race time data]). This puts the race time into seconds. Then I had to divide this time by 3600 (seconds in a day) to be able to format it in something a runner would recognize (you don't have to do this if you want to work strictly in seconds). In this case, I did a custom format of h:m:ss. You can then use this calculation in other calculations like pace per mile. Hope this helps. I am now trying to figure out what kind of visualizations to create now that I have workable data.