string to datetime conversion

hi,
you should use DateDiff method for your purpose.

for eg.

SELECT DATEDIFF(DAY, GETDATE(), GETDATE() + 1) AS DayDiff
SELECT DATEDIFF(MINUTE, GETDATE(), GETDATE() + 1) AS MinuteDiff
SELECT DATEDIFF(SECOND, GETDATE(), GETDATE() + 1) AS SecondDiff
SELECT DATEDIFF(WEEK, GETDATE(), GETDATE() + 1) AS WeekDiff
SELECT DATEDIFF(HOUR, GETDATE(), GETDATE() + 1) AS HourDiff

and about how to convert to date time visit -

SQL Server Functions that helps to convert date and time values to and from string literals and other date and time formats.[^]

And this would help you to convert datetime..
C# Date Time Parser[^]
EDIT:
To save timespan in database view..
http://stackoverflow.com/questions/718332/what-is-the-best-way-to-represent-a-timespan-in-sql-server-ce[^]
http://stackoverflow.com/questions/8503825/what-is-the-correct-sql-type-to-store-a-net-timespan-with-values-240000[^]

DateTime startTime = Convert.ToDateTime("11 Aug 2013 13:10 PM");
DateTime endTime = Convert.ToDateTime("15 Sep 2013 16:20 PM");

//We subtract the time.
TimeSpan span = endTime.Subtract(startTime);

//This will just return the difference in Time
Response.Write("Time Difference (seconds): " + span.Seconds + Environment.NewLine);
Response.Write("Time Difference (minutes): " + span.Minutes + Environment.NewLine);
Response.Write("Time Difference (hours): " + span.Hours + Environment.NewLine);
Response.Write("Time Difference (days): " + span.Days + Environment.NewLine);