Can I see how long a child has been reading for?

No, you can't see the length of time a child has been reading. You can see how many pages that have read though by hovering over the circle on the class reading page. This will show you the number of pages logged for that reading session. 

You can also see a running total of the number of pages and reading logs on the class reading page, next to the current book list. 

Some of our schools log reading in school too. So they use the home filter so they can see how many reading sessions have taken place just at home.