Why does it say that? I have the student license but I thought I have it forever
That just means that you can stay offline until the 25th. After that, you need to let Rhino go online to verify the license on the license server.
Your Rhino license does not expire. It can be installed in two ways:
One way is as a stand alone license on a single computer. Once it is installed on that computer it can only be used on that computer. After installation no internet access is needed. If you need to transfer the license to a different computer then you will need to contact McNeel and I believe you will also internet access.
Another way is to use the Cloud Zoo. With the license installed on the Cloud Zoo the computer using the license needs periodic access to the internet. It if very easy to use a license on a different computer if the license is in the Cloud Zoo as long as both computers have internet access. There is no need to contact McNeel to move the license when it is in the Cloud Zoo. Note that your educational license can only be used by you, not by anyone else. You cannot transfer your educational license to anyone else.