Piwik on Intranet - Unique Visits

We are using Piwik on our intranet and seem to have run into an interesting situation.

We would like to determine whether our site is accessed multiple times throughout the day by a large population or just a small subset (e.g. a specific job function) accessing it frequently.

All our employees should be accessing the site at least once per day (the site should open when each person logs in every morning). As I understand it, Piwik adds a cookie to the computer to track returning users. Since this cookie remains on each employee’s computer, it looks like all visitors through the day are returning users even though the total number of visits could be driven by only a dozen people.

I think the solution to this is to set the cookie to expire after a day.

Does anyone have any thoughts on this strategy? Is there a better one or am I completely misunderstanding how Piwik works?

Also, if this strategy works, where can I find the settings to alter the life of the cookie? Is it somewhere in the admin section or would I have to alter one of the classes. I am very comfortable with PHP.

You can change the tracking cookie expire time by adding in your config.ini.php

[Tracker]
; by default, the Piwik tracking cookie expires in 2 years
cookie_expire = 63072000