Well you dont 
Simply becase the SQL Timestamp is not a date and time. It is a common mistake that most people do.
The SQL Timestamp is merely a versioning of a record in SQL and cannot be converted into a date and/or time. In the most current SQL versions the field is renamed to ROWVERSION in order to remove the confusion.
Thomas Hejlsberg wrote this some time back:
Ok, let me be more precise. Timestamp and rowversion are exactly the same thing on SQL Server. The unfortunate situation is that ISO standards describe SQL Timestamps as something related to date/time whereas MSSQL server decided to implement this as a simple counter. DB2, Oracle and other relational databases uses an actual timestamp (point in time) for timestamp.
Over time this has caused some confusion since developers using other databases as “used” to be able to extract date/time info from a timestamp, which is not possible on MSSQL.
Therefore MSSQL introduced the more correct name Rowversion to describe the same thing.
Furthermore the syntax when creating a table with a timestamp differs a litte from syntax creating a table with at rowversion (name of the column not needed when using timestamp)