Ok 

Follow this logic

You are presumably only interested in Today

so your select Query can exclude datesearlier than Today

Thus Where Getdate() minus 1 day 

Now your example is restricted to only hour 20

SELECT DATEPART(hh,adate) as interestedhour
FROM TblSys
WHERE DATEPART(hh,adate) = '20' and adate > GetDate()-1


This works

Roland