First off, why is less than 30cc/hour bad? It tells us that the kidneys are not being adequately perfused or drained. So while 50cc might be normal, 40cc is an acceptable variation (depending on the patient, of course).
Do people make the same amount of urine throughout the day? No, in fact if people produce enough urine that they have to void at night, this is a deviation from normal. So, there are some times of the day when the patient will produce more than 62cc, and other times when he will produce less than 50cc without there being any problem. The "ideal" amount of urine varies.
As for the acceptable amount of residual urine, that too depends on the patient and the patient's ability to void independently. If there is >100 cc after the patient voids (which is common after a gyn procedure), I ask the patient if she would like to try again, if the bladder feels full, and if she is having discomfort with urination. The ability to empty the bladder by herself is often part of the discharge requirements, so straight cathing a patient for small amounts does not do the patient any favors. The patient needs the bladder to be full (not distended) in order to have the urge to urinate.
Now, if it is a patient who has a history of UTI and bladder stones because they can't empty their bladder, that is a different animal altogether.