Add and Subtract Hours to T-SQL Datetime

Add to 1 hour to the Current Date

 DATEADD(hh,1,getdate())

Subtract 1 hour to the Current Date

 DATEADD(hh,-1,getdate())

Add 1 hour to the Current Time and returns just the time part

select Convert(varchar,( DATEADD(hh,-1,getdate())),8)

Reference
http://msdn.microsoft.com/en-us/library/ms186819.aspx