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