XF 1.1 Users Online For Past 2 Hours?

Hello everyone.

vBulletin had a way you could set the cookie for how long a user remains logged in on the forum. That cookie would die out at whatever second interval that you set up. So, my forum would show everyone that was active in the past 2 hours.

How can I do the same thing here instead of only showing users that have visited in the past 15 minutes?