SQL - Calculate the number of hours between 2 timestamps

Folks,

With SQL,I am trying to determine if the time stamp value in a field
(RVCRDT) within a file (RTPRVER) is more than 8 hours old.

SELECT hour(NOW() - timestamp(RVCRDT)) , timestamp(RVCRDT) as create_date,
NOW()
FROM RTPRVER
WHERE hour(NOW() -  timestamp(RVCRDT)) >= 8

I thought that the HOUR function would give me what I needed, but it seems
to be just subtracting the hours portions of the timestamp fields.

Here's some results that I'm getting.  Obviously, I'm missing something

HOUR   CREATE_DATE            NOW ( )
   8  2006-01-02-00.46.36.000000    2006-06-27-08.47.19.481856
   8  2006-02-12-00.31.37.000000    2006-06-27-08.47.19.481856
   8  2006-02-13-00.17.26.000000    2006-06-27-08.47.19.481856
   8  2006-02-13-00.17.37.000000    2006-06-27-08.47.19.481856
   8  2006-02-13-00.24.35.000000    2006-06-27-08.47.19.481856
   8  2006-02-13-00.36.11.000000    2006-06-27-08.47.19.481856

Any help would be appreciated!!!!!
Thanks
Todd
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