Given the following table ( https://gist.github.com/1712533 ):
step | start_at
------------------------------+---------------------
Startup | 2011-10-01 02:00:00
Find Unique Personas | 2011-10-01 02:01:13
Calculate Loyalty | 2011-10-01 02:01:41
Calculate Social Impressions | 2011-10-01 02:02:38
Calculate Feedback | 2011-10-01 02:03:09
ANALYZE | 2011-10-01 02:09:27
Find the duration of each step.
Window functions will allow you to get the value you need.