If you're using a DATETIME, you can use the DATEPART function to get the hour and group on the value for the hour based on a 24 hour clock.
DATEPART(hh, GETDATE())
You could then group on the hour number and use some kind of CASE statement to give it a pretty name
CASE
...
WHEN DATEPART(hh, GETDATE()) = 14 THEN '2:00pm-3:00pm'
WHEN DATEPART(hh, GETDATE()) = 15 THEN '3:00pm-4:00pm'
...
END
Hope that helps.
John