If you broke that 20.8 hours down into age demographics then the amount of time might not be as grand as it might sound (pun intended). To me at least.
To put that in perspective it's just shy of 3 hours a day across the whole demographic.
If you're in a car or using other forms of public transport to/from work doing an hour round trip, leaves slightly less than a further 2 hours listening time during the day. And that time, I suspect is used for listing to news and traffic before you get on the road/bus or whatever.
For the non-working population I would expect many more hours.