For anything less than 24 hours, you can do this:
SELECT
CONVERT(varchar(8), DATEADD(SECOND, DATEDIFF(SECOND, segstart, segstop), 0), 8)
FROM (
SELECT CAST('20130906 09:28:00' AS datetime) AS segstart, CAST('20130906 09:37:22' AS datetime) AS segstop
) AS test_data
Edit: Added test data.
SQL DBA,SQL Server MVP(07, 08, 09) "It's a dog-eat-dog world, and I'm wearing Milk-Bone underwear." "Norm", on "Cheers". Also from "Cheers", from "Carla": "You need to know 3 things about Tortelli men: Tortelli men draw women like flies; Tortelli men treat women like flies; Tortelli men's brains are in their flies".