I am not an expert on this at all, but it would something definitely challengeable....the whole thing with criminal law is that the charges or offence are based on MATERIAL facts. For a speeding fine, the material facts would be:
- the TIME of the offence
- the DATE of the offence
- the REGO details of the car
- the MAKE AND MODEL of the car
- the SPEED at which the car was travelling
- WHERE the offence occurred
You get the idea. Generally if they get one of those material facts wrong, then it is open to dispute. It often depends on the facts of the actual case at hand and since there was only one material fact wrong, and that it was, in practical terms, just a use of 12 hour time instead of 24 hour time, it is going to be hard to argue against it... but it is possible. If they had gotten that time wrong on a camera fine, where the alleged offender could not subsantiate it either way, a week later or whatever, then you would have more chance. Or if there were more than one material fact that was wrong would add a lot more to the argument.
It is going to be hard to argue since your dad was pulled over - this means there is a cop who can testify to the actual time - ie 8am or 8pm..... this would not be the case with a camera fine and hence arguable.
You could push it, but it is unlikely anyone would be interested because they WILL look at the reality of the situation (unlike the reverse with us) and all the cop who gave the fine has to do is sign a stat dec and hand in his notebook and it is all over red rover.
As for your Dad speeding, get over it!

I think the definition of "speeding" is the cornerstone of the speeding/road safety debate and I dont believe that just because someone has drawn a line in the sand about what is not and what is speeding means that it applies to all of us. Just because some cop says your Dad was driving at a speed over the posted limit, does not mean he was being reckless, unsafe at all and I think this is the basis of the problem.
But good luck!