I have to store a duration in a SQL Server 2008 database. How is this usually done?
For example I will have to be able to store values like: 5 minutes, 8 hours, 10 days,
One word of caution when using the approach with start and end time is the daylight savings time change. You have to make sure that the SQL Server datatype that you're using is supporting the timezone information. Also, you need to make sure, it supports historical DST changing information. For example, before 2007 in US daylight savings time change rules were different than they are currently.
In our databases we just go for safe approach and store start time, end time and duration in seconds.