How to count each IP every 6 hours since its first timestamp?

[stavc]

Hi,

I recieved the following question which I was not able to answer:

Let's simulate a system that charges each event by its IP (clientip). Each time we encounter an
IP it is charged by 1 cent.
There is however a grace period: whenever an IP is charged, for the subsequent 6 hours it will
not be re-charged again.
What will be the charge for the entire sample data? What is the query used?

*I used the "tutorialdata" dataset.

Thanks

[MayteP]

Can you make some assumptions?