Did you modify the query at all?

Having Datepart(hour) in the Group By should make it just return the hours. I just tested that, and it worked:

create table #T (

ID int identity primary key,

TimeStampUTC datetime);

insert into #T (TimeStampUTC)

select '2008-01-01 05:00:00.000' union all

select '2008-01-01 05:15:00.000' union all

select '2008-01-01 05:30:00.000' union all

select '2008-01-01 05:45:00.000' union all

select '2008-01-01 06:00:00.000' union all

select '2008-01-01 06:15:00.000' union all

select '2008-01-01 06:30:00.000' union all

select '2008-01-01 06:45:00.000' union all

select '2008-01-01 07:00:00.000';

select datepart(hour, TimeStampUTC)

from #T

group by datepart(hour, TimeStampUTC);

I don't have your tables, so I can't test much beyond that, but this gives exactly what it's supposed to, and it should work the same way with your data.

If you didn't modify the query, I need table definitions (create scripts) and sample data (insert scripts), so I can test it.