SELECT 
T1.prv_code, 
DateDiff("h",
(select T2.prv_dvalue from R5PROPERTYVALUES AS T2 where (T2.PRV_PROPERTY = 'UTNCIN' AND T2.prv_code = T1.prv_code)),
(select T3.prv_dvalue from R5PROPERTYVALUES AS T3 where (T3.PRV_PROPERTY = 'UTNCOUT' AND T3.prv_code = T1.prv_code))
) AS Differ
FROM R5PROPERTYVALUES AS T1
GROUP BY 
T1.prv_code
;