Someone with good statics knowlege could calculate how average the block time is really. So normally it should be a Gauss normal distribution with the maximum at 10 mins. But it is not, cause e.g. miners are activated or deactivated and difficulty can not react. Look how many blocks are found exactly 10 mins after the last one or even 11 or 9 min.
There is no maximum on the time between blocks, so there is no maximum at 10 minutes. The distribution time between blocks is not a normal distribution. Rather it is poisson with the true mean at ~9.7 minutes. The difficulty adjusts to make it 10 minutes, but new hardware coming online pulls the time down. Since it is poisson, the time can vary a lot, from 0 minutes to several hours, there is no maximum at 10 minutes.
The true mean for bitcoin since genesis block up to now, is ~9.4 minutes last time I calculated this divergence. How did you get 9.7?