Length of Rhino for Mac license

We are using Rhino for Mac in a classroom environment where students are checking out Rhino for Mac 5 licenses from a Zoo 6 server. The options in the Zoo program are set to enable license check out for 60 days, but for some reason all of the computers that have checked it out only have a 30 day license checked out.

We can check the license in and out to renew it, but I was wondering if I was missing some step that would help us leave the license checked out for longer?

The maximum check out time for Educational licenses is 30 days.
This limitation was added to Zoo 6 based on feedback from other schools and administrators.
There is no way to override it.