Hi,
unfortunately, currently in the Kentico CMS isn't option to track website bounces just top exit pages (
Available reports). But it's possible to write your own solution to handle it. However I will write this as a requirement for the future version.
If you take a look at the DevGuide -
Web analytics API cllasses there are also methods working with time intervals so you can use them to write your own solution in combination with bounces.
I hope this will guide you.
Best regards,
Martin Danko