Apparently if you book a driving test right at the end of the examiners day, it is more likely you will pass. There is more paperwork for a failure than for a pass, and if you get a particularly lazy examiner or one that wants to go home they may disregard some minors and pass you if you were close to passing. Its just an assumption by some of the driving instructors in my family, apparently there is quite a trend.
Obviously this doesn't count if you blatantly failed, just gives you a slightly better chance. I personally think rush hour shouldn't make a difference, it is probably the main time you will be in your car so if you can't manage to pass a test at that time I'm unsure if you should even be on the road. It doesn't actually make much of a difference anyway, if there is nobody on the roads sometimes your faults can be more obvious because the examiners will be solely concentrating on your driving rather than be doing risk assessment to make sure you don't kill anyone.