This is a very tricky question as you can get a lot of answers that will be partially correct.
The best answer in my oppinion is between the range of 7 minutes to around 15 minutes.
The reason why saying just one value isn'the best idea is because, if we have two groups of people, the average for the first group might be 7 minutes, and the average for the second group might be 11 minutes. So it's hard to say the average is 7 minutes. It's better presented in an interval where we can find this number :)
