How to build a "Lead time to contact" report ?

We have leads coming from web forms and until someone take that lead into account and changes the status, it can take hours or even days.

I would like to study in a graph the split per time period needed to answer.

For example this would be:

- answered in a day or less: 123 leads

- answered in 1 day: 85

- 3 days: 52

- ....

Is this even possible ?

Can someone point me into the right direction ?

Thanks,

David